[requirements] - C++17 → C++20

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@@ -1,11 +1,10 @@
 ## Library-wide requirements <a id="requirements">[[requirements]]</a>
-This subclause specifies requirements that apply to the entire
-C++standard library. Clauses  [[language.support]] through  [[thread]]
-and Annex  [[depr]] specify the requirements of individual entities
-within the library.
 Requirements specified in terms of interactions between threads do not
 apply to programs having only a single thread of execution.
 Within this subclause, [[organization]] describes the library’s contents
@@ -15,103 +14,85 @@ constraints on types and functions used with the C++standard library,
 [[constraints]] describes constraints on well-formed C++ programs, and
 [[conforming]] describes constraints on conforming implementations.
 ### Library contents and organization <a id="organization">[[organization]]</a>
-[[contents]] describes the entities and macros defined in the
-C++standard library. [[headers]] lists the standard library headers and
 some constraints on those headers. [[compliance]] lists requirements for
 a freestanding implementation of the C++ standard library.
 #### Library contents <a id="contents">[[contents]]</a>
-The C++standard library provides definitions for the entities and macros
-described in the synopses of the C++standard library headers (
-[[headers]]).
 All library entities except `operator new` and `operator delete` are
 defined within the namespace `std` or namespaces nested within namespace
 `std`.[^12] It is unspecified whether names declared in a specific
 namespace are declared directly in that namespace or in an inline
 namespace inside that namespace.[^13]
 Whenever a name `x` defined in the standard library is mentioned, the
 name `x` is assumed to be fully qualified as `::std::x`, unless
-explicitly described otherwise. For example, if the *Effects:* section
 for library function `F` is described as calling library function `G`,
 the function `::std::G` is meant.
 #### Headers <a id="headers">[[headers]]</a>
 Each element of the C++ standard library is declared or defined (as
 appropriate) in a *header*.[^14]
 The C++ standard library provides the *C++ library headers*, shown in
-Table  [[tab:cpp.library.headers]].
-**Table: C++library headers** <a id="tab:cpp.library.headers">[tab:cpp.library.headers]</a>
-|                        |                      |                      |                   |
-| ---------------------- | -------------------- | -------------------- | ----------------- |
-| `<algorithm>`          | `<future>`           | `<numeric>`          | `<strstream>`     |
-| `<any>`                | `<initializer_list>` | `<optional>`         | `<system_error>`  |
-| `<array>`              | `<iomanip>`          | `<ostream>`          | `<thread>`        |
-| `<atomic>`             | `<ios>`              | `<queue>`            | `<tuple>`         |
-| `<bitset>`             | `<iosfwd>`           | `<random>`           | `<type_traits>`   |
-| `<chrono>`             | `<iostream>`         | `<ratio>`            | `<typeindex>`     |
-| `<codecvt>`            | `<istream>`          | `<regex>`            | `<typeinfo>`      |
-| `<complex>`            | `<iterator>`         | `<scoped_allocator>` | `<unordered_map>` |
-| `<condition_variable>` | `<limits>`           | `<set>`              | `<unordered_set>` |
-| `<deque>`              | `<list>`             | `<shared_mutex>`     | `<utility>`       |
-| `<exception>`          | `<locale>`           | `<sstream>`          | `<valarray>`      |
-| `<execution>`          | `<map>`              | `<stack>`            | `<variant>`       |
-| `<filesystem>`         | `<memory>`           | `<stdexcept>`        | `<vector>`        |
-| `<forward_list>`       | `<memory_resource>`  | `<streambuf>`        |                   |
-| `<fstream>`            | `<mutex>`            | `<string>`           |                   |
-| `<functional>`         | `<new>`              | `<string_view>`      |                   |
 The facilities of the C standard library are provided in the additional
-headers shown in Table  [[tab:cpp.c.headers]]. [^15]
-**Table: C++headers for C library facilities** <a id="tab:cpp.c.headers">[tab:cpp.c.headers]</a>
-|              |               |               |             |             |
-| ------------ | ------------- | ------------- | ----------- | ----------- |
-| `<cassert>`  | `<cinttypes>` | `<csignal>`   | `<cstdio>`  | `<cwchar>`  |
-| `<ccomplex>` | `<ciso646>`   | `<cstdalign>` | `<cstdlib>` | `<cwctype>` |
-| `<cctype>`   | `<climits>`   | `<cstdarg>`   | `<cstring>` |             |
-| `<cerrno>`   | `<clocale>`   | `<cstdbool>`  | `<ctgmath>` |             |
-| `<cfenv>`    | `<cmath>`     | `<cstddef>`   | `<ctime>`   |             |
-| `<cfloat>`   | `<csetjmp>`   | `<cstdint>`   | `<cuchar>`  |             |
-Except as noted in Clauses  [[library]] through  [[thread]] and Annex
-[[depr]], the contents of each header `cname` is the same as that of the
-corresponding header `name.h` as specified in the C standard library
-(Clause  [[intro.refs]]). In the C++standard library, however, the
-declarations (except for names which are defined as macros in C) are
-within namespace scope ([[basic.scope.namespace]]) of the namespace
-`std`. It is unspecified whether these names (including any overloads
-added in Clauses  [[language.support]] through  [[thread]] and Annex
-[[depr]]) are first declared within the global namespace scope and are
-then injected into namespace `std` by explicit *using-declaration*s (
-[[namespace.udecl]]).
 Names which are defined as macros in C shall be defined as macros in the
 C++ standard library, even if C grants license for implementation as
 functions.
-[*Note 1*: The names defined as macros in C include the following:
 `assert`, `offsetof`, `setjmp`, `va_arg`, `va_end`, and
 `va_start`. — *end note*]
 Names that are defined as functions in C shall be defined as functions
 in the C++ standard library.[^16]
-Identifiers that are keywords or operators in C++shall not be defined as
-macros in C++standard library headers.[^17]
 [[depr.c.headers]], C standard library headers, describes the effects of
 using the `name.h` (C header) form in a C++ program.[^18]
 Annex K of the C standard describes a large number of functions, with
@@ -122,115 +103,103 @@ service as the C library function with the unsuffixed name, but
 generally take an additional argument whose value is the size of the
 result array. If any C++ header is included, it is
 *implementation-defined* whether any of these names is declared in the
 global namespace. (None of them is declared in namespace `std`.)
-Table  [[tab:c.annex.k.names]] lists the Annex K names that may be
-declared in some header. These names are also subject to the
-restrictions of  [[macro.names]].
-**Table: C standard Annex K names** <a id="tab:c.annex.k.names">[tab:c.annex.k.names]</a>
-|                        |                            |                |               |
-| ---------------------- | -------------------------- | -------------- | ------------- |
-| `abort_handler_s`      | `mbstowcs_s`               | `strncat_s`    | `vswscanf_s`  |
-| `asctime_s`            | `memcpy_s`                 | `strncpy_s`    | `vwprintf_s`  |
-| `bsearch_s`            | `memmove_s`                | `strtok_s`     | `vwscanf_s`   |
-| `constraint_handler_t` | `memset_s`                 | `swprintf_s`   | `wcrtomb_s`   |
-| `ctime_s`              | `printf_s`                 | `swscanf_s`    | `wcscat_s`    |
-| `errno_t`              | `qsort_s`                  | `tmpfile_s`    | `wcscpy_s`    |
-| `fopen_s`              | `RSIZE_MAX`                | `TMP_MAX_S`    | `wcsncat_s`   |
-| `fprintf_s`            | `rsize_t`                  | `tmpnam_s`     | `wcsncpy_s`   |
-| `freopen_s`            | `scanf_s`                  | `vfprintf_s`   | `wcsnlen_s`   |
-| `fscanf_s`             | `set_constraint_handler_s` | `vfscanf_s`    | `wcsrtombs_s` |
-| `fwprintf_s`           | `snprintf_s`               | `vfwprintf_s`  | `wcstok_s`    |
-| `fwscanf_s`            | `snwprintf_s`              | `vfwscanf_s`   | `wcstombs_s`  |
-| `getenv_s`             | `sprintf_s`                | `vprintf_s`    | `wctomb_s`    |
-| `gets_s`               | `sscanf_s`                 | `vscanf_s`     | `wmemcpy_s`   |
-| `gmtime_s`             | `strcat_s`                 | `vsnprintf_s`  | `wmemmove_s`  |
-| `ignore_handler_s`     | `strcpy_s`                 | `vsnwprintf_s` | `wprintf_s`   |
-| `L_tmpnam_s`           | `strerror_s`               | `vsprintf_s`   | `wscanf_s`    |
-| `localtime_s`          | `strerrorlen_s`            | `vsscanf_s`    |               |
-| `mbsrtowcs_s`          | `strlen_s`                 | `vswprintf_s`  |               |
 #### Freestanding implementations <a id="compliance">[[compliance]]</a>
-Two kinds of implementations are defined: *hosted* and *freestanding* (
-[[intro.compliance]]). For a hosted implementation, this International
-Standard describes the set of available headers.
 A freestanding implementation has an *implementation-defined* set of
-headers. This set shall include at least the headers shown in Table
-[[tab:cpp.headers.freestanding]].
-**Table: C++headers for freestanding implementations** <a id="tab:cpp.headers.freestanding">[tab:cpp.headers.freestanding]</a>
 | Subclause              |                           | Header                                           |
-| --------------------------------------------- | ------------------------- | --------------------------------- |
-|                                               |                           | `<ciso646>`                       |
 | [[support.types]]      | Types                     | `<cstddef>`                                      |
-| [[support.limits]] | Implementation properties | `<cfloat>` `<limits>` `<climits>` |
 | [[cstdint]]            | Integer types             | `<cstdint>`                                      |
 | [[support.start.term]] | Start and termination     | `<cstdlib>`                                      |
 | [[support.dynamic]]    | Dynamic memory management | `<new>`                                          |
 | [[support.rtti]]       | Type identification       | `<typeinfo>`                                     |
 | [[support.exception]]  | Exception handling        | `<exception>`                                    |
 | [[support.initlist]]   | Initializer lists         | `<initializer_list>`                             |
 | [[support.runtime]]    | Other runtime support     | `<cstdarg>`                                      |
 | [[meta]]               | Type traits               | `<type_traits>`                                  |
 | [[atomics]]            | Atomics                   | `<atomic>`                                       |
-| [[depr.cstdalign.syn]], [[depr.cstdbool.syn]] | Deprecated headers        | `<cstdalign>` `<cstdbool>`        |
 The supplied version of the header `<cstdlib>` shall declare at least
 the functions `abort`, `atexit`, `at_quick_exit`, `exit`, and
-`quick_exit` ([[support.start.term]]). The other headers listed in this
-table shall meet the same requirements as for a hosted implementation.
 ### Using the library <a id="using">[[using]]</a>
 #### Overview <a id="using.overview">[[using.overview]]</a>
-This section describes how a C++program gains access to the facilities
-of the C++standard library. [[using.headers]] describes effects during
-translation phase 4, while  [[using.linkage]] describes effects during
-phase 8 ([[lex.phases]]).
 #### Headers <a id="using.headers">[[using.headers]]</a>
 The entities in the C++ standard library are defined in headers, whose
 contents are made available to a translation unit when it contains the
-appropriate `#include` preprocessing directive ([[cpp.include]]).
-A translation unit may include library headers in any order (Clause
-[[lex]]). Each may be included more than once, with no effect different
-from being included exactly once, except that the effect of including
-either `<cassert>` or `<assert.h>` depends each time on the lexically
-current definition of `NDEBUG`.[^19]
 A translation unit shall include a header only outside of any
-declaration or definition, and shall include the header lexically before
-the first reference in that translation unit to any of the entities
-declared in that header. No diagnostic is required.
 #### Linkage <a id="using.linkage">[[using.linkage]]</a>
-Entities in the C++standard library have external linkage (
-[[basic.link]]). Unless otherwise specified, objects and functions have
-the default `extern "C++"` linkage ([[dcl.link]]).
 Whether a name from the C standard library declared with external
 linkage has `extern "C"` or `extern "C++"` linkage is
 *implementation-defined*. It is recommended that an implementation use
 `extern "C++"` linkage for this purpose.[^20]
-Objects and functions defined in the library and required by a
-C++program are included in the program prior to program startup.
-See also replacement functions ([[replacement.functions]]), runtime
-changes ([[handler.functions]]).
 ### Requirements on types and expressions <a id="utility.requirements">[[utility.requirements]]</a>
 [[utility.arg.requirements]] describes requirements on types and
 expressions used to instantiate templates defined in the C++ standard
@@ -244,74 +213,74 @@ allocators.
 #### Template argument requirements <a id="utility.arg.requirements">[[utility.arg.requirements]]</a>
 The template definitions in the C++ standard library refer to various
 named requirements whose details are set out in Tables
-[[tab:equalitycomparable]]– [[tab:destructible]]. In these tables, `T`
-is an object or reference type to be supplied by a C++program
-instantiating a template; `a`, `b`, and `c` are values of type (possibly
-`const`) `T`; `s` and `t` are modifiable lvalues of type `T`; `u`
-denotes an identifier; `rv` is an rvalue of type `T`; and `v` is an
 lvalue of type (possibly `const`) `T` or an rvalue of type `const T`.
 In general, a default constructor is not required. Certain container
 class member function signatures specify `T()` as a default argument.
-`T()` shall be a well-defined expression ([[dcl.init]]) if one of those
-signatures is called using the default argument ([[dcl.fct.default]]).
-**Table: `EqualityComparable` requirements** <a id="equalitycomparable">[equalitycomparable]</a>
 | Expression | Return type |
 | ---------- | ----------- |
 | `a == b`   | convertible to `bool` | `==` is an equivalence relation, that is, it has the following properties: For all `a`, `a == a`.; If `a == b`, then `b == a`.; If `a == b` and `b == c`, then `a == c`. |
-**Table: `LessThanComparable` requirements** <a id="lessthancomparable">[lessthancomparable]</a>
 | Expression | Return type           | Requirement                                            |
-| ---------- | --------------------- | --------------------------------------------------------- |
-| `a < b`    | convertible to `bool` | `<` is a strict weak ordering relation~([[alg.sorting]]) |
-**Table: `DefaultConstructible` requirements** <a id="defaultconstructible">[defaultconstructible]</a>
 | Expression     | Post-condition                                                      |
 | -------------- | ------------------------------------------------------------------- |
 | `T t;`         | object `t` is default-initialized                                   |
 | `T u{};`       | object `u` is value-initialized or aggregate-initialized            |
 | `T()`<br>`T{}` | an object of type `T` is value-initialized or aggregate-initialized |
 [*Note 1*: `rv` must still meet the requirements of the library
 component that is using it. The operations listed in those requirements
 must work as specified whether `rv` has been moved from or
 not. — *end note*]
-**Table: `CopyConstructible` requirements (in addition to `MoveConstructible`)** <a id="copyconstructible">[copyconstructible]</a>
 | Expression | Post-condition                                            |
 | ---------- | --------------------------------------------------------- |
 | `T u = v;` | the value of `v` is unchanged and is equivalent to ` u`   |
 | `T(v)`     | the value of `v` is unchanged and is equivalent to `T(v)` |
 [*Note 2*:  `rv` must still meet the requirements of the library
 component that is using it, whether or not `t` and `rv` refer to the
 same object. The operations listed in those requirements must work as
 specified whether `rv` has been moved from or not. — *end note*]
-**Table: `CopyAssignable` requirements (in addition to `MoveAssignable`)** <a id="copyassignable">[copyassignable]</a>
 | Expression | Return type | Return value | Post-condition                                          |
 | ---------- | ----------- | ------------ | ------------------------------------------------------- |
 | `t = v`    | `T&`        | `t`          | `t` is equivalent to `v`, the value of `v` is unchanged |
-**Table: `Destructible` requirements** <a id="destructible">[destructible]</a>
-| Expression | Post-condition                                                        |
-| ---------- | --------------------------------------------------------------------- |
-| `u.~T()`   | All resources owned by `u` are reclaimed, no exception is propagated. |
-#### `Swappable` requirements <a id="swappable.requirements">[[swappable.requirements]]</a>
 This subclause provides definitions for swappable types and expressions.
 In these definitions, let `t` denote an expression of type `T`, and let
 `u` denote an expression of type `U`.
@@ -324,16 +293,15 @@ An object `t` is *swappable with* an object `u` if and only if:
     and
   - the object referred to by `u` has the value originally held by `t`.
 The context in which `swap(t, u)` and `swap(u, t)` are evaluated shall
 ensure that a binary non-member function named “swap” is selected via
-overload resolution ([[over.match]]) on a candidate set that includes:
-- the two `swap` function templates defined in `<utility>` (
-  [[utility]]) and
-- the lookup set produced by argument-dependent lookup (
-  [[basic.lookup.argdep]]).
 [*Note 1*: If `T` and `U` are both fundamental types or arrays of
 fundamental types and the declarations from the header `<utility>` are
 in scope, the overall lookup set described above is equivalent to that
 of the qualified name lookup applied to the expression `std::swap(t, u)`
@@ -344,14 +312,13 @@ swappable requirement includes the header `<utility>` to ensure an
 appropriate evaluation context. — *end note*]
 An rvalue or lvalue `t` is *swappable* if and only if `t` is swappable
 with any rvalue or lvalue, respectively, of type `T`.
-A type `X` satisfying any of the iterator requirements (
-[[iterator.requirements]]) satisfies the requirements of
-`ValueSwappable` if, for any dereferenceable object `x` of type `X`,
-`*x` is swappable.
 [*Example 1*:
 User code can ensure that the evaluation of `swap` calls is performed in
 an appropriate context under the various conditions as follows:
@@ -369,12 +336,12 @@ void value_swap(T&& t, U&& u) {
 // Requires: lvalues of T shall be swappable.
 template<class T>
 void lv_swap(T& t1, T& t2) {
   using std::swap;
-  swap(t1, t2);                                 // OK: uses swappable conditions for
-}                                               // lvalues of type T
 namespace N {
   struct A { int m; };
   struct Proxy { A* a; };
   Proxy proxy(A& a) { return Proxy{ &a }; }
@@ -397,103 +364,102 @@ int main() {
 }
 ```
 — *end example*]
-#### `NullablePointer` requirements <a id="nullablepointer.requirements">[[nullablepointer.requirements]]</a>
-A `NullablePointer` type is a pointer-like type that supports null
-values. A type `P` meets the requirements of `NullablePointer` if:
-- `P` satisfies the requirements of `EqualityComparable`,
- `DefaultConstructible`, `CopyConstructible`, `CopyAssignable`, and
- `Destructible`,
-- lvalues of type `P` are swappable ([[swappable.requirements]]),
-- the expressions shown in Table  [[tab:nullablepointer]] are valid and
- have the indicated semantics, and
-- `P` satisfies all the other requirements of this subclause.
 A value-initialized object of type `P` produces the null value of the
 type. The null value shall be equivalent only to itself. A
 default-initialized object of type `P` may have an indeterminate value.
 [*Note 1*: Operations involving indeterminate values may cause
 undefined behavior. — *end note*]
 An object `p` of type `P` can be contextually converted to `bool`
-(Clause  [[conv]]). The effect shall be as if `p != nullptr` had been
-evaluated in place of `p`.
-No operation which is part of the `NullablePointer` requirements shall
-exit via an exception.
-In Table  [[tab:nullablepointer]], `u` denotes an identifier, `t`
-denotes a non-`const` lvalue of type `P`, `a` and `b` denote values of
-type (possibly `const`) `P`, and `np` denotes a value of type (possibly
 `const`) `std::nullptr_t`.
-**Table: `NullablePointer` requirements** <a id="nullablepointer">[nullablepointer]</a>
-| | | |
-| -------------- | ---------------------------------- | ---------------------------------- |
-| `P u(np);`<br> |                                    | Postconditions: `u == nullptr`     |
 | `P u = np;`    |                                    |                             |
-| `P(np)`        |                                    | Postconditions: `P(np) == nullptr` |
-| `t = np`       | `P&`                               | Postconditions: `t == nullptr`     |
 | `a != b`       | contextually convertible to `bool` | `!(a == b)`                 |
 | `a == np`      | contextually convertible to `bool` | `a == P()`                  |
 | `np == a`      |                                    |                             |
 | `a != np`      | contextually convertible to `bool` | `!(a == np)`                |
 | `np != a`      |                                    |                             |
-#### Hash requirements <a id="hash.requirements">[[hash.requirements]]</a>
-A type `H` meets the `Hash` requirements if:
-- it is a function object type ([[function.objects]]),
-- it satisfies the requirements of `CopyConstructible` and
- `Destructible` ([[utility.arg.requirements]]), and
-- the expressions shown in Table  [[tab:hash]] are valid and have the
   indicated semantics.
 Given `Key` is an argument type for function objects of type `H`, in
-Table  [[tab:hash]] `h` is a value of type (possibly `const`) `H`, `u`
-is an lvalue of type `Key`, and `k` is a value of a type convertible to
 (possibly `const`) `Key`.
 [*Note 1*: Thus all evaluations of the expression `h(k)` with the same
 value for `k` yield the same result for a given execution of the
 program. — *end note*]
-#### Allocator requirements <a id="allocator.requirements">[[allocator.requirements]]</a>
 The library describes a standard set of requirements for *allocators*,
 which are class-type objects that encapsulate the information about an
 allocation model. This information includes the knowledge of pointer
 types, the type of their difference, the type of the size of objects in
 this allocation model, as well as the memory allocation and deallocation
-primitives for it. All of the string types (Clause  [[strings]]),
-containers (Clause  [[containers]]) (except array), string buffers and
-string streams (Clause  [[input.output]]), and `match_results` (Clause
-[[re]]) are parameterized in terms of allocators.
-The class template `allocator_traits` ([[allocator.traits]]) supplies a
-uniform interface to all allocator types. Table  [[tab:desc.var.def]]
-describes the types manipulated through allocators. Table
-[[tab:utilities.allocator.requirements]] describes the requirements on
-allocator types and thus on types used to instantiate
-`allocator_traits`. A requirement is optional if the last column of
-Table  [[tab:utilities.allocator.requirements]] specifies a default for
-a given expression. Within the standard library `allocator_traits`
-template, an optional requirement that is not supplied by an allocator
-is replaced by the specified default expression. A user specialization
-of `allocator_traits` may provide different defaults and may provide
 defaults for different requirements than the primary template. Within
-Tables  [[tab:desc.var.def]] and
-[[tab:utilities.allocator.requirements]], the use of `move` and
-`forward` always refers to `std::move` and `std::forward`, respectively.
 [*Note 1*: If `n == 0`, the return value is unspecified. — *end note*]
 Note A: The member class template `rebind` in the table above is
 effectively a typedef template.
@@ -509,29 +475,36 @@ and `Allocator` does not supply a `rebind` member template, the standard
 `allocator_traits` template uses `SomeAllocator<U, Args>` in place of
 `Allocator::{}rebind<U>::other` by default. For allocator types that are
 not template instantiations of the above form, no default is provided.
 Note B: If `X::propagate_on_container_copy_assignment::value` is `true`,
-`X` shall satisfy the `CopyAssignable` requirements (Table
-[[tab:copyassignable]]) and the copy operation shall not throw
 exceptions. If `X::propagate_on_container_move_assignment::value` is
-`true`, `X` shall satisfy the `MoveAssignable` requirements (Table
-[[tab:moveassignable]]) and the move operation shall not throw
 exceptions. If `X::propagate_on_container_swap::value` is `true`,
-lvalues of type `X` shall be swappable ([[swappable.requirements]]) and
 the `swap` operation shall not throw exceptions.
-An allocator type `X` shall satisfy the requirements of
-`CopyConstructible` ([[utility.arg.requirements]]). The `X::pointer`,
 `X::const_pointer`, `X::void_pointer`, and `X::const_void_pointer` types
-shall satisfy the requirements of `NullablePointer` (
-[[nullablepointer.requirements]]). No constructor, comparison function,
-copy operation, move operation, or swap operation on these pointer types
 shall exit via an exception. `X::pointer` and `X::const_pointer` shall
-also satisfy the requirements for a random access iterator (
-[[random.access.iterators]]) and of a contiguous iterator (
-[[iterator.requirements.general]]).
 Let `x1` and `x2` denote objects of (possibly different) types
 `X::void_pointer`, `X::const_void_pointer`, `X::pointer`, or
 `X::const_pointer`. Then, `x1` and `x2` are *equivalently-valued*
 pointer values, if and only if both `x1` and `x2` can be explicitly
@@ -570,25 +543,32 @@ An allocator may constrain the types on which it can be instantiated and
 the arguments for which its `construct` or `destroy` members may be
 called. If a type cannot be used with a particular allocator, the
 allocator class or the call to `construct` or `destroy` may fail to
 instantiate.
 [*Example 1*:
 The following is an allocator class template supporting the minimal
-interface that satisfies the requirements of Table
-[[tab:utilities.allocator.requirements]]:
 ``` cpp
 template<class Tp>
 struct SimpleAllocator {
   typedef Tp value_type;
   SimpleAllocator(ctor args);
   template<class T> SimpleAllocator(const SimpleAllocator<T>& other);
-  Tp* allocate(std::size_t n);
   void deallocate(Tp* p, std::size_t n);
 };
 template<class T, class U>
 bool operator==(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
@@ -596,52 +576,51 @@ template <class T, class U>
 bool operator!=(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
 ```
 — *end example*]
-If the alignment associated with a specific over-aligned type is not
-supported by an allocator, instantiation of the allocator for that type
-may fail. The allocator also may silently ignore the requested
-alignment.
-[*Note 3*: Additionally, the member function `allocate` for that type
-may fail by throwing an object of type `bad_alloc`. — *end note*]
 ##### Allocator completeness requirements <a id="allocator.requirements.completeness">[[allocator.requirements.completeness]]</a>
-If `X` is an allocator class for type `T`, `X` additionally satisfies
-the allocator completeness requirements if, whether or not `T` is a
-complete type:
 - `X` is a complete type, and
-- all the member types of `allocator_traits<X>` ([[allocator.traits]])
   other than `value_type` are complete types.
 ### Constraints on programs <a id="constraints">[[constraints]]</a>
 #### Overview <a id="constraints.overview">[[constraints.overview]]</a>
-This section describes restrictions on C++programs that use the
-facilities of the C++standard library. The following subclauses specify
-constraints on the program’s use of namespaces ([[namespace.std]]), its
-use of various reserved names ([[reserved.names]]), its use of
-headers ([[alt.headers]]), its use of standard library classes as base
-classes ([[derived.classes]]), its definitions of replacement
-functions ([[replacement.functions]]), and its installation of handler
-functions during execution ([[handler.functions]]).
 #### Namespace use <a id="namespace.constraints">[[namespace.constraints]]</a>
 ##### Namespace `std` <a id="namespace.std">[[namespace.std]]</a>
-The behavior of a C++program is undefined if it adds declarations or
-definitions to namespace `std` or to a namespace within namespace `std`
-unless otherwise specified. A program may add a template specialization
-for any standard library template to namespace `std` only if the
-declaration depends on a user-defined type and the specialization meets
-the standard library requirements for the original template and is not
-explicitly prohibited.[^21]
 The behavior of a C++ program is undefined if it declares
 - an explicit specialization of any member function of a standard
   library class template, or
@@ -649,33 +628,62 @@ The behavior of a C++program is undefined if it declares
   standard library class or class template, or
 - an explicit or partial specialization of any member class template of
   a standard library class or class template, or
 - a deduction guide for any standard library class template.
-A program may explicitly instantiate a template defined in the standard
-library only if the declaration depends on the name of a user-defined
-type and the instantiation meets the standard library requirements for
-the original template.
 A translation unit shall not declare namespace `std` to be an inline
-namespace ([[namespace.def]]).
 ##### Namespace `posix` <a id="namespace.posix">[[namespace.posix]]</a>
 The behavior of a C++ program is undefined if it adds declarations or
 definitions to namespace `posix` or to a namespace within namespace
 `posix` unless otherwise specified. The namespace `posix` is reserved
 for use by ISO/IEC 9945 and other POSIX standards.
 ##### Namespaces for future standardization <a id="namespace.future">[[namespace.future]]</a>
-Top level namespaces with a name starting with `std` and followed by a
-non-empty sequence of digits are reserved for future standardization.
-The behavior of a C++program is undefined if it adds declarations or
-definitions to such a namespace.
-[*Example 1*: The top level namespace `std2` is reserved for use by
 future revisions of this International Standard. — *end example*]
 #### Reserved names <a id="reserved.names">[[reserved.names]]</a>
 The C++ standard library reserves the following kinds of names:
@@ -692,101 +700,133 @@ is undefined.
 In namespace `std`, the following names are reserved for previous
 standardization:
 - `auto_ptr`,
 - `binary_function`,
 - `bind1st`,
 - `bind2nd`,
 - `binder1st`,
 - `binder2nd`,
 - `const_mem_fun1_ref_t`,
 - `const_mem_fun1_t`,
 - `const_mem_fun_ref_t`,
 - `const_mem_fun_t`,
 - `get_unexpected`,
 - `mem_fun1_ref_t`,
 - `mem_fun1_t`,
 - `mem_fun_ref_t`,
 - `mem_fun_ref`,
 - `mem_fun_t`,
 - `mem_fun`,
 - `pointer_to_binary_function`,
 - `pointer_to_unary_function`,
 - `ptr_fun`,
 - `random_shuffle`,
 - `set_unexpected`,
 - `unary_function`,
 - `unexpected`, and
 - `unexpected_handler`.
 ##### Macro names <a id="macro.names">[[macro.names]]</a>
 A translation unit that includes a standard library header shall not
 `#define` or `#undef` names declared in any standard library header.
 A translation unit shall not `#define` or `#undef` names lexically
-identical to keywords, to the identifiers listed in Table
-[[tab:identifiers.special]], or to the *attribute-token*s described in
-[[dcl.attr]].
 ##### External linkage <a id="extern.names">[[extern.names]]</a>
 Each name declared as an object with external linkage in a header is
 reserved to the implementation to designate that library object with
-external linkage, [^22] both in namespace `std` and in the global
 namespace.
 Each global function signature declared with external linkage in a
 header is reserved to the implementation to designate that function
-signature with external linkage.[^23]
 Each name from the C standard library declared with external linkage is
 reserved to the implementation for use as a name with `extern "C"`
 linkage, both in namespace `std` and in the global namespace.
 Each function signature from the C standard library declared with
 external linkage is reserved to the implementation for use as a function
-signature with both `extern "C"` and `extern "C++"` linkage,[^24] or as
 a name of namespace scope in the global namespace.
 ##### Types <a id="extern.types">[[extern.types]]</a>
-For each type T from the C standard library,[^25] the types `::T` and
 `std::T` are reserved to the implementation and, when defined, `::T`
 shall be identical to `std::T`.
 ##### User-defined literal suffixes <a id="usrlit.suffix">[[usrlit.suffix]]</a>
-Literal suffix identifiers ([[over.literal]]) that do not start with an
 underscore are reserved for future standardization.
 #### Headers <a id="alt.headers">[[alt.headers]]</a>
 If a file with a name equivalent to the derived file name for one of the
 C++ standard library headers is not provided as part of the
 implementation, and a file with that name is placed in any of the
-standard places for a source file to be included ([[cpp.include]]), the
 behavior is undefined.
 #### Derived classes <a id="derived.classes">[[derived.classes]]</a>
-Virtual member function signatures defined for a base class in the
-C++standard library may be overridden in a derived class defined in the
-program ([[class.virtual]]).
 #### Replacement functions <a id="replacement.functions">[[replacement.functions]]</a>
-Clauses  [[language.support]] through  [[thread]] and Annex  [[depr]]
-describe the behavior of numerous functions defined by the C++standard
-library. Under some circumstances, however, certain of these function
-descriptions also apply to replacement functions defined in the
-program ([[definitions]]).
-A C++program may provide the definition for any of the following dynamic
-memory allocation function signatures declared in header `<new>` (
-[[basic.stc.dynamic]], [[support.dynamic]]):
 ``` cpp
 operator new(std::size_t)
 operator new(std::size_t, std::align_val_t)
 operator new(std::size_t, const std::nothrow_t&)
@@ -817,19 +857,19 @@ operator delete[](void*, std::size_t, std::align_val_t)
 operator delete[](void*, const std::nothrow_t&)
 operator delete[](void*, std::align_val_t, const std::nothrow_t&)
 ```
 The program’s definitions are used instead of the default versions
-supplied by the implementation ([[support.dynamic]]). Such replacement
-occurs prior to program startup ([[basic.def.odr]], [[basic.start]]).
-The program’s declarations shall not be specified as `inline`. No
-diagnostic is required.
 #### Handler functions <a id="handler.functions">[[handler.functions]]</a>
 The C++ standard library provides a default version of the following
-handler function (Clause  [[language.support]]):
 - `terminate_handler`
 A C++ program may install different handler functions during execution,
 by supplying a pointer to a function defined in the program or the
@@ -855,34 +895,34 @@ function.
 #### Other functions <a id="res.on.functions">[[res.on.functions]]</a>
 In certain cases (replacement functions, handler functions, operations
 on types used to instantiate standard library template components), the
 C++ standard library depends on components supplied by a C++ program. If
-these components do not meet their requirements, this International
-Standard places no requirements on the implementation.
 In particular, the effects are undefined in the following cases:
-- for replacement functions ([[new.delete]]), if the installed
- replacement function does not implement the semantics of the
- applicable *Required behavior:* paragraph.
-- for handler functions ([[new.handler]], [[terminate.handler]]), if
   the installed handler function does not implement the semantics of the
-  applicable *Required behavior:* paragraph
-- for types used as template arguments when instantiating a template
   component, if the operations on the type do not implement the
   semantics of the applicable *Requirements* subclause (
   [[allocator.requirements]], [[container.requirements]],
   [[iterator.requirements]], [[algorithms.requirements]],
   [[numeric.requirements]]). Operations on such types can report a
   failure by throwing an exception unless otherwise specified.
-- if any replacement function or handler function or destructor
   operation exits via an exception, unless specifically allowed in the
   applicable *Required behavior:* paragraph.
-- if an incomplete type ([[basic.types]]) is used as a template
- argument when instantiating a template component, unless specifically
-  allowed for that component.
 #### Function arguments <a id="res.on.arguments">[[res.on.arguments]]</a>
 Each of the following applies to all arguments to functions defined in
 the C++ standard library, unless explicitly stated otherwise.
@@ -897,74 +937,85 @@ the C++standard library, unless explicitly stated otherwise.
   fact valid.
 - If a function argument binds to an rvalue reference parameter, the
   implementation may assume that this parameter is a unique reference to
   this argument. \[*Note 1*: If the parameter is a generic parameter of
   the form `T&&` and an lvalue of type `A` is bound, the argument binds
-  to an lvalue reference ([[temp.deduct.call]]) and thus is not covered
- by the previous sentence. — *end note*] \[*Note 2*: If a program
- casts an lvalue to an xvalue while passing that lvalue to a library
- function (e.g. by calling the function with the argument
- `std::move(x)`), the program is effectively asking that function to
- treat that lvalue as a temporary. The implementation is free to
- optimize away aliasing checks which might be needed if the argument
- was an lvalue. — *end note*]
 #### Library object access <a id="res.on.objects">[[res.on.objects]]</a>
 The behavior of a program is undefined if calls to standard library
 functions from different threads may introduce a data race. The
 conditions under which this may occur are specified in
 [[res.on.data.races]].
 [*Note 1*: Modifying an object of a standard library type that is
 shared between threads risks undefined behavior unless objects of that
-type are explicitly specified as being sharable without data races or
 the user supplies a locking mechanism. — *end note*]
 If an object of a standard library type is accessed, and the beginning
-of the object’s lifetime ([[basic.life]]) does not happen before the
 access, or the access does not happen before the end of the object’s
 lifetime, the behavior is undefined unless otherwise specified.
 [*Note 2*: This applies even to objects such as mutexes intended for
 thread synchronization. — *end note*]
-#### Requires paragraph <a id="res.on.required">[[res.on.required]]</a>
-Violation of the preconditions specified in a function’s *Requires:*
-paragraph results in undefined behavior unless the function’s *Throws:*
-paragraph specifies throwing an exception when the precondition is
-violated.
 ### Conforming implementations <a id="conforming">[[conforming]]</a>
 #### Overview <a id="conforming.overview">[[conforming.overview]]</a>
-This section describes the constraints upon, and latitude of,
-implementations of the C++standard library.
 An implementation’s use of headers is discussed in  [[res.on.headers]],
 its use of macros in  [[res.on.macro.definitions]], non-member functions
 in  [[global.functions]], member functions in  [[member.functions]],
 data race avoidance in  [[res.on.data.races]], access specifiers in
 [[protection.within.classes]], class derivation in  [[derivation]], and
 exceptions in  [[res.on.exception.handling]].
 #### Headers <a id="res.on.headers">[[res.on.headers]]</a>
-A C++header may include other C++headers. A C++header shall provide the
-declarations and definitions that appear in its synopsis. A C++header
-shown in its synopsis as including other C++headers shall provide the
-declarations and definitions that appear in the synopses of those other
-headers.
 Certain types and macros are defined in more than one header. Every such
 entity shall be defined such that any header that defines it may be
-included after any other header that also defines it (
-[[basic.def.odr]]).
-The C standard library headers ([[depr.c.headers]]) shall include only
 their corresponding C++ standard library header, as described in
 [[headers]].
 #### Restrictions on macro definitions <a id="res.on.macro.definitions">[[res.on.macro.definitions]]</a>
@@ -977,31 +1028,30 @@ suitable for use in `#if` preprocessing directives, unless explicitly
 stated otherwise.
 #### Non-member functions <a id="global.functions">[[global.functions]]</a>
 It is unspecified whether any non-member functions in the C++ standard
-library are defined as `inline` ([[dcl.inline]]).
-A call to a non-member function signature described in Clauses
-[[language.support]] through  [[thread]] and Annex  [[depr]] shall
-behave as if the implementation declared no additional non-member
-function signatures.[^26]
 An implementation shall not declare a non-member function signature with
 additional default arguments.
 Unless otherwise specified, calls made by functions in the standard
 library to non-operator, non-member functions do not use functions from
-another namespace which are found through *argument-dependent name
-lookup* ([[basic.lookup.argdep]]).
 [*Note 1*:
 The phrase “unless otherwise specified” applies to cases such as the
-swappable with requirements ([[swappable.requirements]]). The exception
 for overloaded operators allows argument-dependent lookup in cases like
-that of `ostream_iterator::operator=` ([[ostream.iterator.ops]]):
 *Effects:*
 ``` cpp
 *out_stream << value;
@@ -1013,75 +1063,90 @@ return *this;
 — *end note*]
 #### Member functions <a id="member.functions">[[member.functions]]</a>
 It is unspecified whether any member functions in the C++ standard
-library are defined as `inline` ([[dcl.inline]]).
 For a non-virtual member function described in the C++ standard library,
 an implementation may declare a different set of member function
 signatures, provided that any call to the member function that would
 select an overload from the set of declarations described in this
-International Standard behaves as if that overload were selected.
 [*Note 1*: For instance, an implementation may add parameters with
 default values, or replace a member function with default arguments with
 two or more member functions with equivalent behavior, or add additional
 signatures for a member function name. — *end note*]
 #### Constexpr functions and constructors <a id="constexpr.functions">[[constexpr.functions]]</a>
-This International Standard explicitly requires that certain standard
-library functions are `constexpr` ([[dcl.constexpr]]). An
-implementation shall not declare any standard library function signature
-as `constexpr` except for those where it is explicitly required. Within
-any header that provides any non-defining declarations of constexpr
-functions or constructors an implementation shall provide corresponding
-definitions.
 #### Requirements for stable algorithms <a id="algorithm.stable">[[algorithm.stable]]</a>
 When the requirements for an algorithm state that it is “stable” without
 further elaboration, it means:
-- For the *sort* algorithms the relative order of equivalent elements is
   preserved.
-- For the *remove* and *copy* algorithms the relative order of the
- elements that are not removed is preserved.
-- For the *merge* algorithms, for equivalent elements in the original
- two ranges, the elements from the first range (preserving their
- original order) precede the elements from the second range (preserving
- their original order).
 #### Reentrancy <a id="reentrancy">[[reentrancy]]</a>
-Except where explicitly specified in this International Standard, it is
 *implementation-defined* which functions in the C++ standard library may
 be recursively reentered.
 #### Data race avoidance <a id="res.on.data.races">[[res.on.data.races]]</a>
-This section specifies requirements that implementations shall meet to
-prevent data races ([[intro.multithread]]). Every standard library
 function shall meet each requirement unless otherwise specified.
 Implementations may prevent data races in cases other than those
 specified below.
 A C++ standard library function shall not directly or indirectly access
-objects ([[intro.multithread]]) accessible by threads other than the
 current thread unless the objects are accessed directly or indirectly
 via the function’s arguments, including `this`.
 A C++ standard library function shall not directly or indirectly modify
-objects ([[intro.multithread]]) accessible by threads other than the
 current thread unless the objects are accessed directly or indirectly
 via the function’s non-const arguments, including `this`.
-[*Note 1*: This means, for example, that implementations can’t use a
-static object for internal purposes without synchronization because it
-could cause a data race even in programs that do not explicitly share
-objects between threads. — *end note*]
 A C++ standard library function shall not access objects indirectly
 accessible via its arguments or via elements of its container arguments
 except by invoking functions required by its specification on those
 container elements.
@@ -1098,31 +1163,31 @@ Implementations may share their own internal objects between threads if
 the objects are not visible to users and are protected against data
 races.
 Unless otherwise specified, C++ standard library functions shall perform
 all operations solely within the current thread if those operations have
-effects that are visible ([[intro.multithread]]) to users.
 [*Note 3*: This allows implementations to parallelize operations if
 there are no visible side effects. — *end note*]
 #### Protection within classes <a id="protection.within.classes">[[protection.within.classes]]</a>
 It is unspecified whether any function signature or class described in
-Clauses  [[language.support]] through  [[thread]] and Annex  [[depr]] is
-a `friend` of another class in the C++standard library.
 #### Derived classes <a id="derivation">[[derivation]]</a>
-An implementation may derive any class in the C++standard library from a
-class with a name reserved to the implementation.
 Certain classes defined in the C++ standard library are required to be
-derived from other classes in the C++standard library. An implementation
-may derive such a class directly from the required base or indirectly
-through a hierarchy of base classes with names reserved to the
-implementation.
 In any case:
 - Every base class described as `virtual` shall be virtual;
 - Every base class not specified as `virtual` shall not be virtual;
@@ -1142,13 +1207,13 @@ type.
 Functions from the C standard library shall not throw exceptions [^28]
 except when such a function calls a program-supplied function that
 throws an exception.[^29]
-Destructor operations defined in the C++standard library shall not throw
-exceptions. Every destructor in the C++standard library shall behave as
-if it had a non-throwing exception specification.
 Functions defined in the C++ standard library that do not have a
 *Throws:* paragraph but do have a potentially-throwing exception
 specification may throw *implementation-defined* exceptions. [^30]
 Implementations should report errors by throwing exceptions of or
@@ -1160,157 +1225,189 @@ non-virtual function by adding a non-throwing exception specification.
 #### Restrictions on storage of pointers <a id="res.on.pointer.storage">[[res.on.pointer.storage]]</a>
 Objects constructed by the standard library that may hold a
 user-supplied pointer value or an integer of type `std::intptr_t` shall
-store such values in a traceable pointer location (
-[[basic.stc.dynamic.safety]]).
 [*Note 1*: Other libraries are strongly encouraged to do the same,
 since not doing so may result in accidental use of pointers that are not
 safely derived. Libraries that store pointers outside the user’s address
 space should make it appear that they are stored and retrieved from a
 traceable pointer location. — *end note*]
 #### Value of error codes <a id="value.error.codes">[[value.error.codes]]</a>
 Certain functions in the C++ standard library report errors via a
-`std::error_code` ([[syserr.errcode.overview]]) object. That object’s
 `category()` member shall return `std::system_category()` for errors
 originating from the operating system, or a reference to an
 *implementation-defined* `error_category` object for errors originating
 elsewhere. The implementation shall define the possible values of
 `value()` for each of these error categories.
 [*Example 1*: For operating systems that are based on POSIX,
-implementations are encouraged to define the `std::system_category()`
-values as identical to the POSIX `errno` values, with additional values
-as defined by the operating system’s documentation. Implementations for
-operating systems that are not based on POSIX are encouraged to define
-values identical to the operating system’s values. For errors that do
-not originate from the operating system, the implementation may provide
-enums for the associated values. — *end example*]
 #### Moved-from state of library types <a id="lib.types.movedfrom">[[lib.types.movedfrom]]</a>
-Objects of types defined in the C++standard library may be moved from (
-[[class.copy]]). Move operations may be explicitly specified or
 implicitly generated. Unless otherwise specified, such moved-from
 objects shall be placed in a valid but unspecified state.
 <!-- Link reference definitions -->
 [alg.c.library]: algorithms.md#alg.c.library
 [alg.sorting]: algorithms.md#alg.sorting
 [algorithm.stable]: #algorithm.stable
 [algorithms]: algorithms.md#algorithms
 [algorithms.requirements]: algorithms.md#algorithms.requirements
-[alloc.errors]: language.md#alloc.errors
 [allocator.requirements]: #allocator.requirements
 [allocator.requirements.completeness]: #allocator.requirements.completeness
 [allocator.traits]: utilities.md#allocator.traits
 [alt.headers]: #alt.headers
 [atomics]: atomics.md#atomics
-[bad.alloc]: language.md#bad.alloc
 [basic.def.odr]: basic.md#basic.def.odr
 [basic.fundamental]: basic.md#basic.fundamental
 [basic.life]: basic.md#basic.life
 [basic.link]: basic.md#basic.link
 [basic.lookup.argdep]: basic.md#basic.lookup.argdep
 [basic.scope.namespace]: basic.md#basic.scope.namespace
 [basic.start]: basic.md#basic.start
 [basic.stc.dynamic]: basic.md#basic.stc.dynamic
 [basic.stc.dynamic.safety]: basic.md#basic.stc.dynamic.safety
 [basic.types]: basic.md#basic.types
 [bitmask.types]: #bitmask.types
 [byte.strings]: #byte.strings
-[c.locales]: localization.md#c.locales
-[c.strings]: strings.md#c.strings
 [character.seq]: #character.seq
-[class.conv.ctor]: special.md#class.conv.ctor
-[class.copy]: special.md#class.copy
-[class.ctor]: special.md#class.ctor
-[class.dtor]: special.md#class.dtor
 [class.mem]: class.md#class.mem
 [class.mfct]: class.md#class.mfct
 [class.this]: class.md#class.this
 [class.virtual]: class.md#class.virtual
 [compliance]: #compliance
 [conforming]: #conforming
 [conforming.overview]: #conforming.overview
 [constexpr.functions]: #constexpr.functions
 [constraints]: #constraints
 [constraints.overview]: #constraints.overview
 [container.requirements]: containers.md#container.requirements
 [containers]: containers.md#containers
 [contents]: #contents
-[conv]: conv.md#conv
 [conventions]: #conventions
 [cpp.include]: cpp.md#cpp.include
-[cstdint]: language.md#cstdint
 [dcl.array]: dcl.md#dcl.array
 [dcl.attr]: dcl.md#dcl.attr
 [dcl.constexpr]: dcl.md#dcl.constexpr
 [dcl.fct.default]: dcl.md#dcl.fct.default
 [dcl.init]: dcl.md#dcl.init
 [dcl.init.list]: dcl.md#dcl.init.list
 [dcl.inline]: dcl.md#dcl.inline
 [dcl.link]: dcl.md#dcl.link
 [definitions]: #definitions
 [depr]: future.md#depr
 [depr.c.headers]: future.md#depr.c.headers
-[depr.cstdalign.syn]: future.md#depr.cstdalign.syn
-[depr.cstdbool.syn]: future.md#depr.cstdbool.syn
 [derivation]: #derivation
 [derived.classes]: #derived.classes
 [description]: #description
 [diagnostics]: diagnostics.md#diagnostics
 [enumerated.types]: #enumerated.types
 [except]: except.md#except
 [expos.only.types]: #expos.only.types
 [expr.cond]: expr.md#expr.cond
 [expr.const]: expr.md#expr.const
 [expr.delete]: expr.md#expr.delete
 [expr.eq]: expr.md#expr.eq
 [expr.new]: expr.md#expr.new
 [expr.rel]: expr.md#expr.rel
 [extern.names]: #extern.names
 [extern.types]: #extern.types
 [function.objects]: utilities.md#function.objects
 [functions.within.classes]: #functions.within.classes
 [global.functions]: #global.functions
 [handler.functions]: #handler.functions
 [hash.requirements]: #hash.requirements
 [headers]: #headers
 [input.output]: input.md#input.output
 [intro.compliance]: intro.md#intro.compliance
 [intro.defs]: intro.md#intro.defs
-[intro.multithread]: intro.md#intro.multithread
 [intro.refs]: intro.md#intro.refs
 [iterator.requirements]: iterators.md#iterator.requirements
-[iterator.requirements.general]: iterators.md#iterator.requirements.general
 [iterators]: iterators.md#iterators
-[language.support]: language.md#language.support
-[lex]: lex.md#lex
 [lex.phases]: lex.md#lex.phases
 [lib.types.movedfrom]: #lib.types.movedfrom
 [library]: #library
 [library.c]: #library.c
 [library.general]: #library.general
 [locales]: localization.md#locales
 [localization]: localization.md#localization
 [macro.names]: #macro.names
 [member.functions]: #member.functions
 [meta]: utilities.md#meta
 [multibyte.strings]: #multibyte.strings
 [namespace.constraints]: #namespace.constraints
 [namespace.def]: dcl.md#namespace.def
 [namespace.future]: #namespace.future
 [namespace.posix]: #namespace.posix
 [namespace.std]: #namespace.std
 [namespace.udecl]: dcl.md#namespace.udecl
-[new.delete]: language.md#new.delete
-[new.handler]: language.md#new.handler
 [nullablepointer.requirements]: #nullablepointer.requirements
 [numeric.requirements]: numerics.md#numeric.requirements
 [numerics]: numerics.md#numerics
 [objects.within.classes]: #objects.within.classes
 [organization]: #organization
@@ -1318,71 +1415,73 @@ objects shall be placed in a valid but unspecified state.
 [over.literal]: over.md#over.literal
 [over.match]: over.md#over.match
 [over.oper]: over.md#over.oper
 [protection.within.classes]: #protection.within.classes
 [random.access.iterators]: iterators.md#random.access.iterators
 [re]: re.md#re
 [reentrancy]: #reentrancy
 [replacement.functions]: #replacement.functions
 [requirements]: #requirements
 [res.on.arguments]: #res.on.arguments
 [res.on.data.races]: #res.on.data.races
 [res.on.exception.handling]: #res.on.exception.handling
 [res.on.functions]: #res.on.functions
 [res.on.headers]: #res.on.headers
 [res.on.macro.definitions]: #res.on.macro.definitions
 [res.on.objects]: #res.on.objects
 [res.on.pointer.storage]: #res.on.pointer.storage
-[res.on.required]: #res.on.required
 [reserved.names]: #reserved.names
 [std.exceptions]: diagnostics.md#std.exceptions
 [stream.types]: input.md#stream.types
 [strings]: strings.md#strings
 [structure]: #structure
 [structure.elements]: #structure.elements
 [structure.requirements]: #structure.requirements
 [structure.see.also]: #structure.see.also
 [structure.specifications]: #structure.specifications
 [structure.summary]: #structure.summary
-[support.dynamic]: language.md#support.dynamic
-[support.exception]: language.md#support.exception
-[support.initlist]: language.md#support.initlist
-[support.limits]: language.md#support.limits
-[support.rtti]: language.md#support.rtti
-[support.runtime]: language.md#support.runtime
-[support.start.term]: language.md#support.start.term
-[support.types]: language.md#support.types
 [swappable.requirements]: #swappable.requirements
 [syserr]: diagnostics.md#syserr
 [syserr.errcode.overview]: diagnostics.md#syserr.errcode.overview
-[tab:c.annex.k.names]: #tab:c.annex.k.names
-[tab:copyassignable]: #tab:copyassignable
-[tab:cpp.c.headers]: #tab:cpp.c.headers
-[tab:cpp.headers.freestanding]: #tab:cpp.headers.freestanding
-[tab:cpp.library.headers]: #tab:cpp.library.headers
-[tab:desc.var.def]: #tab:desc.var.def
-[tab:destructible]: #tab:destructible
-[tab:equalitycomparable]: #tab:equalitycomparable
-[tab:hash]: #tab:hash
-[tab:identifiers.special]: lex.md#tab:identifiers.special
-[tab:library.categories]: #tab:library.categories
-[tab:moveassignable]: #tab:moveassignable
-[tab:nullablepointer]: #tab:nullablepointer
-[tab:utilities.allocator.requirements]: #tab:utilities.allocator.requirements
 [temp.deduct.call]: temp.md#temp.deduct.call
 [template.bitset]: utilities.md#template.bitset
-[terminate.handler]: language.md#terminate.handler
 [thread]: thread.md#thread
 [type.descriptions]: #type.descriptions
 [type.descriptions.general]: #type.descriptions.general
 [using]: #using
 [using.headers]: #using.headers
 [using.linkage]: #using.linkage
 [using.overview]: #using.overview
 [usrlit.suffix]: #usrlit.suffix
 [utilities]: utilities.md#utilities
-[utility]: utilities.md#utility
 [utility.arg.requirements]: #utility.arg.requirements
 [utility.requirements]: #utility.requirements
 [value.error.codes]: #value.error.codes
 [zombie.names]: #zombie.names
@@ -1395,60 +1494,60 @@ objects shall be placed in a valid but unspecified state.
 [^3]: To save space, items that do not apply to a class are omitted. For
     example, if a class does not specify any comparison functions, there
     will be no “Comparison functions” subclause.
-[^4]: To save space, items that do not apply to a function are omitted.
-    For example, if a function does not specify any further
- preconditions, there will be no *Requires:* paragraph.
 [^5]: This simplifies the presentation of complexity requirements in
     some cases.
 [^6]: Examples from  [[utility.requirements]] include:
- `EqualityComparable`, `LessThanComparable`, `CopyConstructible`.
-    Examples from  [[iterator.requirements]] include: `InputIterator`,
- `ForwardIterator`.
-[^7]: Such as an integer type, with constant integer values (
-    [[basic.fundamental]]).
-[^8]: declared in `<clocale>` ([[c.locales]]).
 [^9]: Many of the objects manipulated by function signatures declared in
-    `<cstring>` ([[c.strings]]) are character sequences or NTBSs. The
- size of some of these character sequences is limited by a length
- value, maintained separately from the character sequence.
-[^10]: A string literal, such as `"abc"`, is a static NTBS.
 [^11]: An NTBS that contains characters only from the basic execution
     character set is also an NTMBS. Each multibyte character then
     consists of a single byte.
-[^12]: The C standard library headers (Annex  [[depr.c.headers]]) also
- define names within the global namespace, while the C++headers for C
-    library facilities ([[headers]]) may also define names within the
     global namespace.
 [^13]: This gives implementers freedom to use inline namespaces to
     support multiple configurations of the library.
 [^14]: A header is not necessarily a source file, nor are the sequences
     delimited by `<` and `>` in header names necessarily valid source
-    file names ([[cpp.include]]).
 [^15]: It is intentional that there is no C++ header for any of these C
     headers: `<stdatomic.h>`, `<stdnoreturn.h>`, `<threads.h>`.
 [^16]: This disallows the practice, allowed in C, of providing a masking
     macro in addition to the function prototype. The only way to achieve
     equivalent inline behavior in C++ is to provide a definition as an
     extern inline function.
-[^17]: In particular, including the standard header `<iso646.h>` or
- `<ciso646>` has no effect.
 [^18]: The `".h"` headers dump all their names into the global
     namespace, whereas the newer forms keep their names in namespace
     `std`. Therefore, the newer forms are the preferred forms for all
     uses except for C++ programs which are intended to be strictly
@@ -1460,43 +1559,50 @@ objects shall be placed in a valid but unspecified state.
     from the C standard library is by including the header that declares
     it, notwithstanding the latitude granted in 7.1.4 of the C Standard.
 [^21]: Any library code that instantiates other library templates must
     be prepared to work adequately with any user-supplied specialization
-    that meets the minimum requirements of this International Standard.
-[^22]: The list of such reserved names includes `errno`, declared or
     defined in `<cerrno>`.
-[^23]: The list of such reserved function signatures with external
     linkage includes `setjmp(jmp_buf)`, declared or defined in
     `<csetjmp>`, and `va_end(va_list)`, declared or defined in
     `<cstdarg>`.
-[^24]: The function signatures declared in `<cuchar>`, `<cwchar>`, and
     `<cwctype>` are always reserved, notwithstanding the restrictions
     imposed in subclause 4.5.1 of Amendment 1 to the C Standard for
     these headers.
-[^25]: These types are `clock_t`, `div_t`, `FILE`, `fpos_t`, `lconv`,
-    `ldiv_t`, `mbstate_t`, `ptrdiff_t`, `sig_atomic_t`, `size_t`,
-    `time_t`, `tm`, `va_list`, `wctrans_t`, `wctype_t`, and `wint_t`.
 [^26]: A valid C++ program always calls the expected library non-member
     function. An implementation may also define additional non-member
     functions that would otherwise not be called by a valid C++ program.
 [^27]: There is an implicit exception to this rule for types that are
-    described as synonyms for basic integral types, such as `size_t` (
-    [[support.types]]) and `streamoff` ([[stream.types]]).
 [^28]: That is, the C library functions can all be treated as if they
     are marked `noexcept`. This allows implementations to make
     performance optimizations based on the absence of exceptions at
     runtime.
-[^29]: The functions `qsort()` and `bsearch()` ([[alg.c.library]]) meet
     this condition.
 [^30]: In particular, they can report a failure to allocate storage by
     throwing an exception of type `bad_alloc`, or a class derived from
-    `bad_alloc` ([[bad.alloc]]).

 ## Library-wide requirements <a id="requirements">[[requirements]]</a>
+This subclause specifies requirements that apply to the entire C++
+standard library. [[support]] through [[thread]] and [[depr]] specify
+the requirements of individual entities within the library.
 Requirements specified in terms of interactions between threads do not
 apply to programs having only a single thread of execution.
 Within this subclause, [[organization]] describes the library’s contents
 [[constraints]] describes constraints on well-formed C++ programs, and
 [[conforming]] describes constraints on conforming implementations.
 ### Library contents and organization <a id="organization">[[organization]]</a>
+[[contents]] describes the entities and macros defined in the C++
+standard library. [[headers]] lists the standard library headers and
 some constraints on those headers. [[compliance]] lists requirements for
 a freestanding implementation of the C++ standard library.
 #### Library contents <a id="contents">[[contents]]</a>
+The C++ standard library provides definitions for the entities and
+macros described in the synopses of the C++ standard library headers
+[[headers]], unless otherwise specified.
 All library entities except `operator new` and `operator delete` are
 defined within the namespace `std` or namespaces nested within namespace
 `std`.[^12] It is unspecified whether names declared in a specific
 namespace are declared directly in that namespace or in an inline
 namespace inside that namespace.[^13]
 Whenever a name `x` defined in the standard library is mentioned, the
 name `x` is assumed to be fully qualified as `::std::x`, unless
+explicitly described otherwise. For example, if the *Effects:* element
 for library function `F` is described as calling library function `G`,
 the function `::std::G` is meant.
 #### Headers <a id="headers">[[headers]]</a>
 Each element of the C++ standard library is declared or defined (as
 appropriate) in a *header*.[^14]
 The C++ standard library provides the *C++ library headers*, shown in
+[[headers.cpp]].
 The facilities of the C standard library are provided in the additional
+headers shown in [[headers.cpp.c]]. [^15]
+The headers listed in [[headers.cpp]], or, for a freestanding
+implementation, the subset of such headers that are provided by the
+implementation, are collectively known as the
+*importable C++ library headers*.
+[*Note 1*: Importable C++ library headers can be imported as module
+units [[module.import]]. — *end note*]
+[*Example 1*:
+``` cpp
+import <vector>;                // imports the <vector> header unit
+std::vector<int> vi;            // OK
+```
+— *end example*]
+Except as noted in [[library]] through [[thread]] and [[depr]], the
+contents of each header `cname` is the same as that of the corresponding
+header `name.h` as specified in the C standard library [[intro.refs]].
+In the C++ standard library, however, the declarations (except for names
+which are defined as macros in C) are within namespace scope
+[[basic.scope.namespace]] of the namespace `std`. It is unspecified
+whether these names (including any overloads added in [[support]]
+through [[thread]] and [[depr]]) are first declared within the global
+namespace scope and are then injected into namespace `std` by explicit
+*using-declaration*s [[namespace.udecl]].
 Names which are defined as macros in C shall be defined as macros in the
 C++ standard library, even if C grants license for implementation as
 functions.
+[*Note 2*: The names defined as macros in C include the following:
 `assert`, `offsetof`, `setjmp`, `va_arg`, `va_end`, and
 `va_start`. — *end note*]
 Names that are defined as functions in C shall be defined as functions
 in the C++ standard library.[^16]
+Identifiers that are keywords or operators in C++ shall not be defined
+as macros in C++ standard library headers.[^17]
 [[depr.c.headers]], C standard library headers, describes the effects of
 using the `name.h` (C header) form in a C++ program.[^18]
 Annex K of the C standard describes a large number of functions, with
 generally take an additional argument whose value is the size of the
 result array. If any C++ header is included, it is
 *implementation-defined* whether any of these names is declared in the
 global namespace. (None of them is declared in namespace `std`.)
+[[c.annex.k.names]] lists the Annex K names that may be declared in some
+header. These names are also subject to the restrictions of
+[[macro.names]].
 #### Freestanding implementations <a id="compliance">[[compliance]]</a>
+Two kinds of implementations are defined: *hosted* and *freestanding*
+[[intro.compliance]]; the kind of the implementation is
+*implementation-defined*. For a hosted implementation, this document
+describes the set of available headers.
 A freestanding implementation has an *implementation-defined* set of
+headers. This set shall include at least the headers shown in
+[[headers.cpp.fs]].
+**Table: C++ headers for freestanding implementations** <a id="headers.cpp.fs">[headers.cpp.fs]</a>
 | Subclause              |                           | Header                                           |
+| ---------------------- | ------------------------- | ------------------------------------------------ |
 | [[support.types]]      | Types                     | `<cstddef>`                                      |
+| [[support.limits]] | Implementation properties | `<cfloat>`, `<climits>`, `<limits>`, `<version>` |
 | [[cstdint]]            | Integer types             | `<cstdint>`                                      |
 | [[support.start.term]] | Start and termination     | `<cstdlib>`                                      |
 | [[support.dynamic]]    | Dynamic memory management | `<new>`                                          |
 | [[support.rtti]]       | Type identification       | `<typeinfo>`                                     |
+| [[support.srcloc]]     | Source location           | `<source_location>`                              |
 | [[support.exception]]  | Exception handling        | `<exception>`                                    |
 | [[support.initlist]]   | Initializer lists         | `<initializer_list>`                             |
+| [[cmp]]                | Comparisons               | `<compare>`                                      |
+| [[support.coroutine]]  | Coroutines support        | `<coroutine>`                                    |
 | [[support.runtime]]    | Other runtime support     | `<cstdarg>`                                      |
+| [[concepts]]           | Concepts library          | `<concepts>`                                     |
 | [[meta]]               | Type traits               | `<type_traits>`                                  |
+| [[bit]]                | Bit manipulation          | `<bit>`                                          |
 | [[atomics]]            | Atomics                   | `<atomic>`                                       |
 The supplied version of the header `<cstdlib>` shall declare at least
 the functions `abort`, `atexit`, `at_quick_exit`, `exit`, and
+`quick_exit` [[support.start.term]]. The supplied version of the header
+`<atomic>` shall meet the same requirements as for a hosted
+implementation except that support for always lock-free integral atomic
+types [[atomics.lockfree]] is *implementation-defined*, and whether or
+not the type aliases `atomic_signed_lock_free` and
+`atomic_unsigned_lock_free` are defined [[atomics.alias]] is
+*implementation-defined*. The other headers listed in this table shall
+meet the same requirements as for a hosted implementation.
 ### Using the library <a id="using">[[using]]</a>
 #### Overview <a id="using.overview">[[using.overview]]</a>
+Subclause [[using]] describes how a C++ program gains access to the
+facilities of the C++ standard library. [[using.headers]] describes
+effects during translation phase 4, while  [[using.linkage]] describes
+effects during phase 8 [[lex.phases]].
 #### Headers <a id="using.headers">[[using.headers]]</a>
 The entities in the C++ standard library are defined in headers, whose
 contents are made available to a translation unit when it contains the
+appropriate `#include` preprocessing directive [[cpp.include]] or the
+appropriate `import` declaration [[module.import]].
+A translation unit may include library headers in any order
+[[lex.separate]]. Each may be included more than once, with no effect
+different from being included exactly once, except that the effect of
+including either `<cassert>` or `<assert.h>` depends each time on the
+lexically current definition of `NDEBUG`.[^19]
 A translation unit shall include a header only outside of any
+declaration or definition and, in the case of a module unit, only in its
+*global-module-fragment*, and shall include the header or import the
+corresponding header unit lexically before the first reference in that
+translation unit to any of the entities declared in that header. No
+diagnostic is required.
 #### Linkage <a id="using.linkage">[[using.linkage]]</a>
+Entities in the C++ standard library have external linkage
+[[basic.link]]. Unless otherwise specified, objects and functions have
+the default `extern "C++"` linkage [[dcl.link]].
 Whether a name from the C standard library declared with external
 linkage has `extern "C"` or `extern "C++"` linkage is
 *implementation-defined*. It is recommended that an implementation use
 `extern "C++"` linkage for this purpose.[^20]
+Objects and functions defined in the library and required by a C++
+program are included in the program prior to program startup.
+See also replacement functions [[replacement.functions]], runtime
+changes [[handler.functions]].
 ### Requirements on types and expressions <a id="utility.requirements">[[utility.requirements]]</a>
 [[utility.arg.requirements]] describes requirements on types and
 expressions used to instantiate templates defined in the C++ standard
 #### Template argument requirements <a id="utility.arg.requirements">[[utility.arg.requirements]]</a>
 The template definitions in the C++ standard library refer to various
 named requirements whose details are set out in Tables
+[[tab:cpp17.equalitycomparable]]– [[tab:cpp17.destructible]]. In these
+tables, `T` is an object or reference type to be supplied by a C++
+program instantiating a template; `a`, `b`, and `c` are values of type
+(possibly `const`) `T`; `s` and `t` are modifiable lvalues of type `T`;
+`u` denotes an identifier; `rv` is an rvalue of type `T`; and `v` is an
 lvalue of type (possibly `const`) `T` or an rvalue of type `const T`.
 In general, a default constructor is not required. Certain container
 class member function signatures specify `T()` as a default argument.
+`T()` shall be a well-defined expression [[dcl.init]] if one of those
+signatures is called using the default argument [[dcl.fct.default]].
+**Table: Cpp17EqualityComparable requirements** <a id="cpp17.equalitycomparable">[cpp17.equalitycomparable]</a>
 | Expression | Return type |
 | ---------- | ----------- |
 | `a == b`   | convertible to `bool` | `==` is an equivalence relation, that is, it has the following properties: For all `a`, `a == a`.; If `a == b`, then `b == a`.; If `a == b` and `b == c`, then `a == c`. |
+**Table: Cpp17LessThanComparable requirements** <a id="cpp17.lessthancomparable">[cpp17.lessthancomparable]</a>
 | Expression | Return type           | Requirement                                            |
+| ---------- | --------------------- | ------------------------------------------------------ |
+| `a < b`    | convertible to `bool` | `<` is a strict weak ordering relation [[alg.sorting]] |
+**Table: Cpp17DefaultConstructible requirements** <a id="cpp17.defaultconstructible">[cpp17.defaultconstructible]</a>
 | Expression     | Post-condition                                                      |
 | -------------- | ------------------------------------------------------------------- |
 | `T t;`         | object `t` is default-initialized                                   |
 | `T u{};`       | object `u` is value-initialized or aggregate-initialized            |
 | `T()`<br>`T{}` | an object of type `T` is value-initialized or aggregate-initialized |
 [*Note 1*: `rv` must still meet the requirements of the library
 component that is using it. The operations listed in those requirements
 must work as specified whether `rv` has been moved from or
 not. — *end note*]
+**Table: Cpp17CopyConstructible requirements (in addition to Cpp17MoveConstructible)** <a id="cpp17.copyconstructible">[cpp17.copyconstructible]</a>
 | Expression | Post-condition                                            |
 | ---------- | --------------------------------------------------------- |
 | `T u = v;` | the value of `v` is unchanged and is equivalent to ` u`   |
 | `T(v)`     | the value of `v` is unchanged and is equivalent to `T(v)` |
 [*Note 2*:  `rv` must still meet the requirements of the library
 component that is using it, whether or not `t` and `rv` refer to the
 same object. The operations listed in those requirements must work as
 specified whether `rv` has been moved from or not. — *end note*]
+**Table: Cpp17CopyAssignable requirements (in addition to Cpp17MoveAssignable)** <a id="cpp17.copyassignable">[cpp17.copyassignable]</a>
 | Expression | Return type | Return value | Post-condition                                          |
 | ---------- | ----------- | ------------ | ------------------------------------------------------- |
 | `t = v`    | `T&`        | `t`          | `t` is equivalent to `v`, the value of `v` is unchanged |
+[*Note 3*: Array types and non-object types are not
+*Cpp17Destructible*. — *end note*]
+#### Swappable requirements <a id="swappable.requirements">[[swappable.requirements]]</a>
 This subclause provides definitions for swappable types and expressions.
 In these definitions, let `t` denote an expression of type `T`, and let
 `u` denote an expression of type `U`.
     and
   - the object referred to by `u` has the value originally held by `t`.
 The context in which `swap(t, u)` and `swap(u, t)` are evaluated shall
 ensure that a binary non-member function named “swap” is selected via
+overload resolution [[over.match]] on a candidate set that includes:
+- the two `swap` function templates defined in `<utility>` and
+- the lookup set produced by argument-dependent lookup
+  [[basic.lookup.argdep]].
 [*Note 1*: If `T` and `U` are both fundamental types or arrays of
 fundamental types and the declarations from the header `<utility>` are
 in scope, the overall lookup set described above is equivalent to that
 of the qualified name lookup applied to the expression `std::swap(t, u)`
 appropriate evaluation context. — *end note*]
 An rvalue or lvalue `t` is *swappable* if and only if `t` is swappable
 with any rvalue or lvalue, respectively, of type `T`.
+A type `X` meeting any of the iterator requirements
+[[iterator.requirements]] meets the *Cpp17ValueSwappable* requirements
+if, for any dereferenceable object `x` of type `X`, `*x` is swappable.
 [*Example 1*:
 User code can ensure that the evaluation of `swap` calls is performed in
 an appropriate context under the various conditions as follows:
 // Requires: lvalues of T shall be swappable.
 template<class T>
 void lv_swap(T& t1, T& t2) {
   using std::swap;
+  swap(t1, t2);                                 // OK: uses swappable conditions for lvalues of type T
+}
 namespace N {
   struct A { int m; };
   struct Proxy { A* a; };
   Proxy proxy(A& a) { return Proxy{ &a }; }
 }
 ```
 — *end example*]
+#### *Cpp17NullablePointer* requirements <a id="nullablepointer.requirements">[[nullablepointer.requirements]]</a>
+A *Cpp17NullablePointer* type is a pointer-like type that supports null
+values. A type `P` meets the *Cpp17NullablePointer* requirements if:
+- `P` meets the *Cpp17EqualityComparable*, *Cpp17DefaultConstructible*,
+ *Cpp17CopyConstructible*, *Cpp17CopyAssignable*, and
+ *Cpp17Destructible* requirements,
+- lvalues of type `P` are swappable [[swappable.requirements]],
+- the expressions shown in [[cpp17.nullablepointer]] are valid and have
+  the indicated semantics, and
+- `P` meets all the other requirements of this subclause.
 A value-initialized object of type `P` produces the null value of the
 type. The null value shall be equivalent only to itself. A
 default-initialized object of type `P` may have an indeterminate value.
 [*Note 1*: Operations involving indeterminate values may cause
 undefined behavior. — *end note*]
 An object `p` of type `P` can be contextually converted to `bool`
+[[conv]]. The effect shall be as if `p != nullptr` had been evaluated in
+place of `p`.
+No operation which is part of the *Cpp17NullablePointer* requirements
+shall exit via an exception.
+In [[cpp17.nullablepointer]], `u` denotes an identifier, `t` denotes a
+non-`const` lvalue of type `P`, `a` and `b` denote values of type
+(possibly `const`) `P`, and `np` denotes a value of type (possibly
 `const`) `std::nullptr_t`.
+**Table: Cpp17NullablePointer requirements** <a id="cpp17.nullablepointer">[cpp17.nullablepointer]</a>
+| Expression     | Return type                        | Operational semantics       |
+| -------------- | ---------------------------------- | --------------------------- |
+| `P u(np);`<br> |                                    | Ensures: `u == nullptr`     |
 | `P u = np;`    |                                    |                             |
+| `P(np)`        |                                    | Ensures: `P(np) == nullptr` |
+| `t = np`       | `P&`                               | Ensures: `t == nullptr`     |
 | `a != b`       | contextually convertible to `bool` | `!(a == b)`                 |
 | `a == np`      | contextually convertible to `bool` | `a == P()`                  |
 | `np == a`      |                                    |                             |
 | `a != np`      | contextually convertible to `bool` | `!(a == np)`                |
 | `np != a`      |                                    |                             |
+#### *Cpp17Hash* requirements <a id="hash.requirements">[[hash.requirements]]</a>
+A type `H` meets the requirements if:
+- it is a function object type [[function.objects]],
+- it meets the *Cpp17CopyConstructible* ([[cpp17.copyconstructible]])
+ and *Cpp17Destructible* ([[cpp17.destructible]]) requirements, and
+- the expressions shown in [[cpp17.hash]] are valid and have the
   indicated semantics.
 Given `Key` is an argument type for function objects of type `H`, in
+[[cpp17.hash]] `h` is a value of type (possibly `const`) `H`, `u` is an
+lvalue of type `Key`, and `k` is a value of a type convertible to
 (possibly `const`) `Key`.
 [*Note 1*: Thus all evaluations of the expression `h(k)` with the same
 value for `k` yield the same result for a given execution of the
 program. — *end note*]
+#### *Cpp17Allocator* requirements <a id="allocator.requirements">[[allocator.requirements]]</a>
 The library describes a standard set of requirements for *allocators*,
 which are class-type objects that encapsulate the information about an
 allocation model. This information includes the knowledge of pointer
 types, the type of their difference, the type of the size of objects in
 this allocation model, as well as the memory allocation and deallocation
+primitives for it. All of the string types [[strings]], containers
+[[containers]] (except `array`), string buffers and string streams
+[[input.output]], and `match_results` [[re]] are parameterized in terms
+of allocators.
+The class template `allocator_traits` [[allocator.traits]] supplies a
+uniform interface to all allocator types. [[allocator.req.var]]
+describes the types manipulated through allocators. [[cpp17.allocator]]
+describes the requirements on allocator types and thus on types used to
+instantiate `allocator_traits`. A requirement is optional if the last
+column of [[cpp17.allocator]] specifies a default for a given
+expression. Within the standard library `allocator_traits` template, an
+optional requirement that is not supplied by an allocator is replaced by
+the specified default expression. A user specialization of
+`allocator_traits` may provide different defaults and may provide
 defaults for different requirements than the primary template. Within
+Tables  [[tab:allocator.req.var]] and  [[tab:cpp17.allocator]], the use
+of `move` and `forward` always refers to `std::move` and `std::forward`,
+respectively.
 [*Note 1*: If `n == 0`, the return value is unspecified. — *end note*]
 Note A: The member class template `rebind` in the table above is
 effectively a typedef template.
 `allocator_traits` template uses `SomeAllocator<U, Args>` in place of
 `Allocator::{}rebind<U>::other` by default. For allocator types that are
 not template instantiations of the above form, no default is provided.
 Note B: If `X::propagate_on_container_copy_assignment::value` is `true`,
+`X` shall meet the *Cpp17CopyAssignable* requirements (
+[[cpp17.copyassignable]]) and the copy operation shall not throw
 exceptions. If `X::propagate_on_container_move_assignment::value` is
+`true`, `X` shall meet the *Cpp17MoveAssignable* requirements (
+[[cpp17.moveassignable]]) and the move operation shall not throw
 exceptions. If `X::propagate_on_container_swap::value` is `true`,
+lvalues of type `X` shall be swappable [[swappable.requirements]] and
 the `swap` operation shall not throw exceptions.
+An allocator type `X` shall meet the *Cpp17CopyConstructible*
+requirements ([[cpp17.copyconstructible]]). The `X::pointer`,
 `X::const_pointer`, `X::void_pointer`, and `X::const_void_pointer` types
+shall meet the *Cpp17NullablePointer* requirements (
+[[cpp17.nullablepointer]]). No constructor, comparison function, copy
+operation, move operation, or swap operation on these pointer types
 shall exit via an exception. `X::pointer` and `X::const_pointer` shall
+also meet the requirements for a *Cpp17RandomAccessIterator*
+[[random.access.iterators]] and the additional requirement that, when
+`a` and `(a + n)` are dereferenceable pointer values for some integral
+value `n`,
+``` cpp
+addressof(*(a + n)) == addressof(*a) + n
+```
+is `true`.
 Let `x1` and `x2` denote objects of (possibly different) types
 `X::void_pointer`, `X::const_void_pointer`, `X::pointer`, or
 `X::const_pointer`. Then, `x1` and `x2` are *equivalently-valued*
 pointer values, if and only if both `x1` and `x2` can be explicitly
 the arguments for which its `construct` or `destroy` members may be
 called. If a type cannot be used with a particular allocator, the
 allocator class or the call to `construct` or `destroy` may fail to
 instantiate.
+If the alignment associated with a specific over-aligned type is not
+supported by an allocator, instantiation of the allocator for that type
+may fail. The allocator also may silently ignore the requested
+alignment.
+[*Note 3*: Additionally, the member function `allocate` for that type
+may fail by throwing an object of type `bad_alloc`. — *end note*]
 [*Example 1*:
 The following is an allocator class template supporting the minimal
+interface that meets the requirements of [[cpp17.allocator]]:
 ``` cpp
 template<class Tp>
 struct SimpleAllocator {
   typedef Tp value_type;
   SimpleAllocator(ctor args);
   template<class T> SimpleAllocator(const SimpleAllocator<T>& other);
+ [[nodiscard]] Tp* allocate(std::size_t n);
   void deallocate(Tp* p, std::size_t n);
 };
 template<class T, class U>
 bool operator==(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
 bool operator!=(const SimpleAllocator<T>&, const SimpleAllocator<U>&);
 ```
 — *end example*]
 ##### Allocator completeness requirements <a id="allocator.requirements.completeness">[[allocator.requirements.completeness]]</a>
+If `X` is an allocator class for type `T`, `X` additionally meets the
+allocator completeness requirements if, whether or not `T` is a complete
+type:
 - `X` is a complete type, and
+- all the member types of `allocator_traits<X>` [[allocator.traits]]
   other than `value_type` are complete types.
 ### Constraints on programs <a id="constraints">[[constraints]]</a>
 #### Overview <a id="constraints.overview">[[constraints.overview]]</a>
+Subclause [[constraints]] describes restrictions on C++ programs that
+use the facilities of the C++ standard library. The following subclauses
+specify constraints on the program’s use of namespaces
+[[namespace.std]], its use of various reserved names [[reserved.names]],
+its use of headers [[alt.headers]], its use of standard library classes
+as base classes [[derived.classes]], its definitions of replacement
+functions [[replacement.functions]], and its installation of handler
+functions during execution [[handler.functions]].
 #### Namespace use <a id="namespace.constraints">[[namespace.constraints]]</a>
 ##### Namespace `std` <a id="namespace.std">[[namespace.std]]</a>
+Unless otherwise specified, the behavior of a C++ program is undefined
+if it adds declarations or definitions to namespace `std` or to a
+namespace within namespace `std`.
+Unless explicitly prohibited, a program may add a template
+specialization for any standard library class template to namespace
+`std` provided that (a) the added declaration depends on at least one
+program-defined type and (b) the specialization meets the standard
+library requirements for the original template.[^21]
+The behavior of a C++ program is undefined if it declares an explicit or
+partial specialization of any standard library variable template, except
+where explicitly permitted by the specification of that variable
+template.
 The behavior of a C++ program is undefined if it declares
 - an explicit specialization of any member function of a standard
   library class template, or
   standard library class or class template, or
 - an explicit or partial specialization of any member class template of
   a standard library class or class template, or
 - a deduction guide for any standard library class template.
+A program may explicitly instantiate a class template defined in the
+standard library only if the declaration (a) depends on the name of at
+least one program-defined type and (b) the instantiation meets the
+standard library requirements for the original template.
+Let `F` denote a standard library function [[global.functions]], a
+standard library static member function, or an instantiation of a
+standard library function template. Unless `F` is designated an
+*addressable function*, the behavior of a C++ program is unspecified
+(possibly ill-formed) if it explicitly or implicitly attempts to form a
+pointer to `F`.
+[*Note 1*: Possible means of forming such pointers include application
+of the unary `&` operator [[expr.unary.op]], `addressof`
+[[specialized.addressof]], or a function-to-pointer standard conversion
+[[conv.func]]. — *end note*]
+Moreover, the behavior of a C++ program is unspecified (possibly
+ill-formed) if it attempts to form a reference to `F` or if it attempts
+to form a pointer-to-member designating either a standard library
+non-static member function [[member.functions]] or an instantiation of a
+standard library member function template.
+Other than in namespace `std` or in a namespace within namespace `std`,
+a program may provide an overload for any library function template
+designated as a *customization point*, provided that (a) the overload’s
+declaration depends on at least one user-defined type and (b) the
+overload meets the standard library requirements for the customization
+point. [^22]
+[*Note 2*: This permits a (qualified or unqualified) call to the
+customization point to invoke the most appropriate overload for the
+given arguments. — *end note*]
 A translation unit shall not declare namespace `std` to be an inline
+namespace [[namespace.def]].
 ##### Namespace `posix` <a id="namespace.posix">[[namespace.posix]]</a>
 The behavior of a C++ program is undefined if it adds declarations or
 definitions to namespace `posix` or to a namespace within namespace
 `posix` unless otherwise specified. The namespace `posix` is reserved
 for use by ISO/IEC 9945 and other POSIX standards.
 ##### Namespaces for future standardization <a id="namespace.future">[[namespace.future]]</a>
+Top-level namespaces whose *namespace-name* consists of `std` followed
+by one or more *digit*s [[lex.name]] are reserved for future
+standardization. The behavior of a C++ program is undefined if it adds
+declarations or definitions to such a namespace.
+[*Example 1*: The top-level namespace `std2` is reserved for use by
 future revisions of this International Standard. — *end example*]
 #### Reserved names <a id="reserved.names">[[reserved.names]]</a>
 The C++ standard library reserves the following kinds of names:
 In namespace `std`, the following names are reserved for previous
 standardization:
 - `auto_ptr`,
+- `auto_ptr_ref`,
 - `binary_function`,
+- `binary_negate`,
 - `bind1st`,
 - `bind2nd`,
 - `binder1st`,
 - `binder2nd`,
 - `const_mem_fun1_ref_t`,
 - `const_mem_fun1_t`,
 - `const_mem_fun_ref_t`,
 - `const_mem_fun_t`,
+- `get_temporary_buffer`,
 - `get_unexpected`,
+- `gets`,
+- `is_literal_type`,
+- `is_literal_type_v`,
 - `mem_fun1_ref_t`,
 - `mem_fun1_t`,
 - `mem_fun_ref_t`,
 - `mem_fun_ref`,
 - `mem_fun_t`,
 - `mem_fun`,
+- `not1`,
+- `not2`,
 - `pointer_to_binary_function`,
 - `pointer_to_unary_function`,
 - `ptr_fun`,
 - `random_shuffle`,
+- `raw_storage_iterator`,
+- `result_of`,
+- `result_of_t`,
+- `return_temporary_buffer`,
 - `set_unexpected`,
 - `unary_function`,
+- `unary_negate`,
+- `uncaught_exception`,
 - `unexpected`, and
 - `unexpected_handler`.
+The following names are reserved as member types for previous
+standardization, and may not be used as a name for object-like macros in
+portable code:
+- `argument_type`,
+- `first_argument_type`,
+- `io_state`,
+- `open_mode`,
+- `second_argument_type`, and
+- `seek_dir`.
+The name `stossc` is reserved as a member function for previous
+standardization, and may not be used as a name for function-like macros
+in portable code.
+The header names `<ccomplex>`, `<ciso646>`, `<cstdalign>`, `<cstdbool>`,
+and `<ctgmath>` are reserved for previous standardization.
 ##### Macro names <a id="macro.names">[[macro.names]]</a>
 A translation unit that includes a standard library header shall not
 `#define` or `#undef` names declared in any standard library header.
 A translation unit shall not `#define` or `#undef` names lexically
+identical to keywords, to the identifiers listed in
+[[lex.name.special]], or to the *attribute-token*s described in
+[[dcl.attr]], except that the names `likely` and `unlikely` may be
+defined as function-like macros  [[cpp.replace]].
 ##### External linkage <a id="extern.names">[[extern.names]]</a>
 Each name declared as an object with external linkage in a header is
 reserved to the implementation to designate that library object with
+external linkage, [^23] both in namespace `std` and in the global
 namespace.
 Each global function signature declared with external linkage in a
 header is reserved to the implementation to designate that function
+signature with external linkage.[^24]
 Each name from the C standard library declared with external linkage is
 reserved to the implementation for use as a name with `extern "C"`
 linkage, both in namespace `std` and in the global namespace.
 Each function signature from the C standard library declared with
 external linkage is reserved to the implementation for use as a function
+signature with both `extern "C"` and `extern "C++"` linkage,[^25] or as
 a name of namespace scope in the global namespace.
 ##### Types <a id="extern.types">[[extern.types]]</a>
+For each type `T` from the C standard library, the types `::T` and
 `std::T` are reserved to the implementation and, when defined, `::T`
 shall be identical to `std::T`.
 ##### User-defined literal suffixes <a id="usrlit.suffix">[[usrlit.suffix]]</a>
+Literal suffix identifiers [[over.literal]] that do not start with an
 underscore are reserved for future standardization.
 #### Headers <a id="alt.headers">[[alt.headers]]</a>
 If a file with a name equivalent to the derived file name for one of the
 C++ standard library headers is not provided as part of the
 implementation, and a file with that name is placed in any of the
+standard places for a source file to be included [[cpp.include]], the
 behavior is undefined.
 #### Derived classes <a id="derived.classes">[[derived.classes]]</a>
+Virtual member function signatures defined for a base class in the C++
+standard library may be overridden in a derived class defined in the
+program [[class.virtual]].
 #### Replacement functions <a id="replacement.functions">[[replacement.functions]]</a>
+[[support]] through [[thread]] and [[depr]] describe the behavior of
+numerous functions defined by the C++ standard library. Under some
+circumstances, however, certain of these function descriptions also
+apply to replacement functions defined in the program [[definitions]].
+A C++ program may provide the definition for any of the following
+dynamic memory allocation function signatures declared in header
+`<new>` ([[basic.stc.dynamic]], [[new.syn]]):
 ``` cpp
 operator new(std::size_t)
 operator new(std::size_t, std::align_val_t)
 operator new(std::size_t, const std::nothrow_t&)
 operator delete[](void*, const std::nothrow_t&)
 operator delete[](void*, std::align_val_t, const std::nothrow_t&)
 ```
 The program’s definitions are used instead of the default versions
+supplied by the implementation [[new.delete]]. Such replacement occurs
+prior to program startup ([[basic.def.odr]], [[basic.start]]). The
+program’s declarations shall not be specified as `inline`. No diagnostic
+is required.
 #### Handler functions <a id="handler.functions">[[handler.functions]]</a>
 The C++ standard library provides a default version of the following
+handler function [[support]]:
 - `terminate_handler`
 A C++ program may install different handler functions during execution,
 by supplying a pointer to a function defined in the program or the
 #### Other functions <a id="res.on.functions">[[res.on.functions]]</a>
 In certain cases (replacement functions, handler functions, operations
 on types used to instantiate standard library template components), the
 C++ standard library depends on components supplied by a C++ program. If
+these components do not meet their requirements, this document places no
+requirements on the implementation.
 In particular, the effects are undefined in the following cases:
+- For replacement functions [[new.delete]], if the installed replacement
+  function does not implement the semantics of the applicable *Required
+  behavior:* paragraph.
+- For handler functions ([[new.handler]], [[terminate.handler]]), if
   the installed handler function does not implement the semantics of the
+  applicable *Required behavior:* paragraph.
+- For types used as template arguments when instantiating a template
   component, if the operations on the type do not implement the
   semantics of the applicable *Requirements* subclause (
   [[allocator.requirements]], [[container.requirements]],
   [[iterator.requirements]], [[algorithms.requirements]],
   [[numeric.requirements]]). Operations on such types can report a
   failure by throwing an exception unless otherwise specified.
+- If any replacement function or handler function or destructor
   operation exits via an exception, unless specifically allowed in the
   applicable *Required behavior:* paragraph.
+- If an incomplete type [[basic.types]] is used as a template argument
+  when instantiating a template component or evaluating a concept,
+ unless specifically allowed for that component.
 #### Function arguments <a id="res.on.arguments">[[res.on.arguments]]</a>
 Each of the following applies to all arguments to functions defined in
 the C++ standard library, unless explicitly stated otherwise.
   fact valid.
 - If a function argument binds to an rvalue reference parameter, the
   implementation may assume that this parameter is a unique reference to
   this argument. \[*Note 1*: If the parameter is a generic parameter of
   the form `T&&` and an lvalue of type `A` is bound, the argument binds
+  to an lvalue reference [[temp.deduct.call]] and thus is not covered by
+  the previous sentence. — *end note*] \[*Note 2*: If a program casts
+  an lvalue to an xvalue while passing that lvalue to a library function
+  (e.g., by calling the function with the argument `std::move(x)`), the
+  program is effectively asking that function to treat that lvalue as a
+  temporary object. The implementation is free to optimize away aliasing
+  checks which might be needed if the argument was an
+  lvalue. — *end note*]
 #### Library object access <a id="res.on.objects">[[res.on.objects]]</a>
 The behavior of a program is undefined if calls to standard library
 functions from different threads may introduce a data race. The
 conditions under which this may occur are specified in
 [[res.on.data.races]].
 [*Note 1*: Modifying an object of a standard library type that is
 shared between threads risks undefined behavior unless objects of that
+type are explicitly specified as being shareable without data races or
 the user supplies a locking mechanism. — *end note*]
 If an object of a standard library type is accessed, and the beginning
+of the object’s lifetime [[basic.life]] does not happen before the
 access, or the access does not happen before the end of the object’s
 lifetime, the behavior is undefined unless otherwise specified.
 [*Note 2*: This applies even to objects such as mutexes intended for
 thread synchronization. — *end note*]
+#### Expects paragraph <a id="res.on.expects">[[res.on.expects]]</a>
+Violation of any preconditions specified in a function’s
+*Preconditions:* element results in undefined behavior.
+#### Semantic requirements <a id="res.on.requirements">[[res.on.requirements]]</a>
+A sequence `Args` of template arguments is said to *model* a concept `C`
+if `Args` satisfies `C` [[temp.constr.decl]] and meets all semantic
+requirements (if any) given in the specification of `C`.
+If the validity or meaning of a program depends on whether a sequence of
+template arguments models a concept, and the concept is satisfied but
+not modeled, the program is ill-formed, no diagnostic required.
+If the semantic requirements of a declaration’s constraints
+[[structure.requirements]] are not modeled at the point of use, the
+program is ill-formed, no diagnostic required.
 ### Conforming implementations <a id="conforming">[[conforming]]</a>
 #### Overview <a id="conforming.overview">[[conforming.overview]]</a>
+Subclause [[conforming]] describes the constraints upon, and latitude
+of, implementations of the C++ standard library.
 An implementation’s use of headers is discussed in  [[res.on.headers]],
 its use of macros in  [[res.on.macro.definitions]], non-member functions
 in  [[global.functions]], member functions in  [[member.functions]],
 data race avoidance in  [[res.on.data.races]], access specifiers in
 [[protection.within.classes]], class derivation in  [[derivation]], and
 exceptions in  [[res.on.exception.handling]].
 #### Headers <a id="res.on.headers">[[res.on.headers]]</a>
+A C++ header may include other C++ headers. A C++ header shall provide
+the declarations and definitions that appear in its synopsis. A C++
+header shown in its synopsis as including other C++ headers shall
+provide the declarations and definitions that appear in the synopses of
+those other headers.
 Certain types and macros are defined in more than one header. Every such
 entity shall be defined such that any header that defines it may be
+included after any other header that also defines it [[basic.def.odr]].
+The C standard library headers [[depr.c.headers]] shall include only
 their corresponding C++ standard library header, as described in
 [[headers]].
 #### Restrictions on macro definitions <a id="res.on.macro.definitions">[[res.on.macro.definitions]]</a>
 stated otherwise.
 #### Non-member functions <a id="global.functions">[[global.functions]]</a>
 It is unspecified whether any non-member functions in the C++ standard
+library are defined as inline [[dcl.inline]].
+A call to a non-member function signature described in [[support]]
+through [[thread]] and [[depr]] shall behave as if the implementation
+declared no additional non-member function signatures.[^26]
 An implementation shall not declare a non-member function signature with
 additional default arguments.
 Unless otherwise specified, calls made by functions in the standard
 library to non-operator, non-member functions do not use functions from
+another namespace which are found through argument-dependent name lookup
+[[basic.lookup.argdep]].
 [*Note 1*:
 The phrase “unless otherwise specified” applies to cases such as the
+swappable with requirements [[swappable.requirements]]. The exception
 for overloaded operators allows argument-dependent lookup in cases like
+that of `ostream_iterator::operator=` [[ostream.iterator.ops]]:
 *Effects:*
 ``` cpp
 *out_stream << value;
 — *end note*]
 #### Member functions <a id="member.functions">[[member.functions]]</a>
 It is unspecified whether any member functions in the C++ standard
+library are defined as inline [[dcl.inline]].
 For a non-virtual member function described in the C++ standard library,
 an implementation may declare a different set of member function
 signatures, provided that any call to the member function that would
 select an overload from the set of declarations described in this
+document behaves as if that overload were selected.
 [*Note 1*: For instance, an implementation may add parameters with
 default values, or replace a member function with default arguments with
 two or more member functions with equivalent behavior, or add additional
 signatures for a member function name. — *end note*]
+#### Friend functions <a id="hidden.friends">[[hidden.friends]]</a>
+Whenever this document specifies a friend declaration of a function or
+function template within a class or class template definition, that
+declaration shall be the only declaration of that function or function
+template provided by an implementation.
+[*Note 1*: In particular, an implementation is not allowed to provide
+an additional declaration of that function or function template at
+namespace scope. — *end note*]
+[*Note 2*: Such a friend function or function template declaration is
+known as a hidden friend, as it is visible neither to ordinary
+unqualified lookup [[basic.lookup.unqual]] nor to qualified lookup
+[[basic.lookup.qual]]. — *end note*]
 #### Constexpr functions and constructors <a id="constexpr.functions">[[constexpr.functions]]</a>
+This document explicitly requires that certain standard library
+functions are `constexpr` [[dcl.constexpr]]. An implementation shall not
+declare any standard library function signature as `constexpr` except
+for those where it is explicitly required. Within any header that
+provides any non-defining declarations of constexpr functions or
+constructors an implementation shall provide corresponding definitions.
 #### Requirements for stable algorithms <a id="algorithm.stable">[[algorithm.stable]]</a>
 When the requirements for an algorithm state that it is “stable” without
 further elaboration, it means:
+- For the sort algorithms the relative order of equivalent elements is
   preserved.
+- For the remove and copy algorithms the relative order of the elements
+  that are not removed is preserved.
+- For the merge algorithms, for equivalent elements in the original two
+  ranges, the elements from the first range (preserving their original
+  order) precede the elements from the second range (preserving their
+  original order).
 #### Reentrancy <a id="reentrancy">[[reentrancy]]</a>
+Except where explicitly specified in this document, it is
 *implementation-defined* which functions in the C++ standard library may
 be recursively reentered.
 #### Data race avoidance <a id="res.on.data.races">[[res.on.data.races]]</a>
+This subclause specifies requirements that implementations shall meet to
+prevent data races [[intro.multithread]]. Every standard library
 function shall meet each requirement unless otherwise specified.
 Implementations may prevent data races in cases other than those
 specified below.
 A C++ standard library function shall not directly or indirectly access
+objects [[intro.multithread]] accessible by threads other than the
 current thread unless the objects are accessed directly or indirectly
 via the function’s arguments, including `this`.
 A C++ standard library function shall not directly or indirectly modify
+objects [[intro.multithread]] accessible by threads other than the
 current thread unless the objects are accessed directly or indirectly
 via the function’s non-const arguments, including `this`.
+[*Note 1*: This means, for example, that implementations can’t use an
+object with static storage duration for internal purposes without
+synchronization because it could cause a data race even in programs that
+do not explicitly share objects between threads. — *end note*]
 A C++ standard library function shall not access objects indirectly
 accessible via its arguments or via elements of its container arguments
 except by invoking functions required by its specification on those
 container elements.
 the objects are not visible to users and are protected against data
 races.
 Unless otherwise specified, C++ standard library functions shall perform
 all operations solely within the current thread if those operations have
+effects that are visible [[intro.multithread]] to users.
 [*Note 3*: This allows implementations to parallelize operations if
 there are no visible side effects. — *end note*]
 #### Protection within classes <a id="protection.within.classes">[[protection.within.classes]]</a>
 It is unspecified whether any function signature or class described in
+[[support]] through [[thread]] and [[depr]] is a friend of another class
+in the C++ standard library.
 #### Derived classes <a id="derivation">[[derivation]]</a>
+An implementation may derive any class in the C++ standard library from
+a class with a name reserved to the implementation.
 Certain classes defined in the C++ standard library are required to be
+derived from other classes in the C++ standard library. An
+implementation may derive such a class directly from the required base
+or indirectly through a hierarchy of base classes with names reserved to
+the implementation.
 In any case:
 - Every base class described as `virtual` shall be virtual;
 - Every base class not specified as `virtual` shall not be virtual;
 Functions from the C standard library shall not throw exceptions [^28]
 except when such a function calls a program-supplied function that
 throws an exception.[^29]
+Destructor operations defined in the C++ standard library shall not
+throw exceptions. Every destructor in the C++ standard library shall
+behave as if it had a non-throwing exception specification.
 Functions defined in the C++ standard library that do not have a
 *Throws:* paragraph but do have a potentially-throwing exception
 specification may throw *implementation-defined* exceptions. [^30]
 Implementations should report errors by throwing exceptions of or
 #### Restrictions on storage of pointers <a id="res.on.pointer.storage">[[res.on.pointer.storage]]</a>
 Objects constructed by the standard library that may hold a
 user-supplied pointer value or an integer of type `std::intptr_t` shall
+store such values in a traceable pointer location
+[[basic.stc.dynamic.safety]].
 [*Note 1*: Other libraries are strongly encouraged to do the same,
 since not doing so may result in accidental use of pointers that are not
 safely derived. Libraries that store pointers outside the user’s address
 space should make it appear that they are stored and retrieved from a
 traceable pointer location. — *end note*]
 #### Value of error codes <a id="value.error.codes">[[value.error.codes]]</a>
 Certain functions in the C++ standard library report errors via a
+`std::error_code` [[syserr.errcode.overview]] object. That object’s
 `category()` member shall return `std::system_category()` for errors
 originating from the operating system, or a reference to an
 *implementation-defined* `error_category` object for errors originating
 elsewhere. The implementation shall define the possible values of
 `value()` for each of these error categories.
 [*Example 1*: For operating systems that are based on POSIX,
+implementations should define the `std::system_category()` values as
+identical to the POSIX `errno` values, with additional values as defined
+by the operating system’s documentation. Implementations for operating
+systems that are not based on POSIX should define values identical to
+the operating system’s values. For errors that do not originate from the
+operating system, the implementation may provide enums for the
+associated values. — *end example*]
 #### Moved-from state of library types <a id="lib.types.movedfrom">[[lib.types.movedfrom]]</a>
+Objects of types defined in the C++ standard library may be moved from
+[[class.copy.ctor]]. Move operations may be explicitly specified or
 implicitly generated. Unless otherwise specified, such moved-from
 objects shall be placed in a valid but unspecified state.
 <!-- Link reference definitions -->
 [alg.c.library]: algorithms.md#alg.c.library
 [alg.sorting]: algorithms.md#alg.sorting
 [algorithm.stable]: #algorithm.stable
 [algorithms]: algorithms.md#algorithms
 [algorithms.requirements]: algorithms.md#algorithms.requirements
+[alloc.errors]: support.md#alloc.errors
+[allocator.req.var]: #allocator.req.var
 [allocator.requirements]: #allocator.requirements
 [allocator.requirements.completeness]: #allocator.requirements.completeness
 [allocator.traits]: utilities.md#allocator.traits
 [alt.headers]: #alt.headers
 [atomics]: atomics.md#atomics
+[atomics.alias]: atomics.md#atomics.alias
+[atomics.lockfree]: atomics.md#atomics.lockfree
+[bad.alloc]: support.md#bad.alloc
 [basic.def.odr]: basic.md#basic.def.odr
 [basic.fundamental]: basic.md#basic.fundamental
 [basic.life]: basic.md#basic.life
 [basic.link]: basic.md#basic.link
 [basic.lookup.argdep]: basic.md#basic.lookup.argdep
+[basic.lookup.qual]: basic.md#basic.lookup.qual
+[basic.lookup.unqual]: basic.md#basic.lookup.unqual
 [basic.scope.namespace]: basic.md#basic.scope.namespace
 [basic.start]: basic.md#basic.start
 [basic.stc.dynamic]: basic.md#basic.stc.dynamic
 [basic.stc.dynamic.safety]: basic.md#basic.stc.dynamic.safety
 [basic.types]: basic.md#basic.types
+[bit]: numerics.md#bit
 [bitmask.types]: #bitmask.types
 [byte.strings]: #byte.strings
+[c.annex.k.names]: #c.annex.k.names
 [character.seq]: #character.seq
+[class.copy.assign]: class.md#class.copy.assign
+[class.copy.ctor]: class.md#class.copy.ctor
+[class.dtor]: class.md#class.dtor
 [class.mem]: class.md#class.mem
 [class.mfct]: class.md#class.mfct
 [class.this]: class.md#class.this
 [class.virtual]: class.md#class.virtual
+[cmp]: support.md#cmp
 [compliance]: #compliance
+[concept.destructible]: concepts.md#concept.destructible
+[concept.invocable]: concepts.md#concept.invocable
+[concept.totallyordered]: concepts.md#concept.totallyordered
+[concepts]: concepts.md#concepts
+[concepts.equality]: concepts.md#concepts.equality
+[concepts.object]: concepts.md#concepts.object
 [conforming]: #conforming
 [conforming.overview]: #conforming.overview
 [constexpr.functions]: #constexpr.functions
 [constraints]: #constraints
 [constraints.overview]: #constraints.overview
 [container.requirements]: containers.md#container.requirements
 [containers]: containers.md#containers
 [contents]: #contents
+[conv]: expr.md#conv
+[conv.func]: expr.md#conv.func
 [conventions]: #conventions
 [cpp.include]: cpp.md#cpp.include
+[cpp.replace]: cpp.md#cpp.replace
+[cpp17.allocator]: #cpp17.allocator
+[cpp17.copyassignable]: #cpp17.copyassignable
+[cpp17.copyconstructible]: #cpp17.copyconstructible
+[cpp17.destructible]: #cpp17.destructible
+[cpp17.hash]: #cpp17.hash
+[cpp17.moveassignable]: #cpp17.moveassignable
+[cpp17.nullablepointer]: #cpp17.nullablepointer
+[cstdint]: support.md#cstdint
+[customization.point.object]: #customization.point.object
 [dcl.array]: dcl.md#dcl.array
 [dcl.attr]: dcl.md#dcl.attr
 [dcl.constexpr]: dcl.md#dcl.constexpr
 [dcl.fct.default]: dcl.md#dcl.fct.default
 [dcl.init]: dcl.md#dcl.init
 [dcl.init.list]: dcl.md#dcl.init.list
 [dcl.inline]: dcl.md#dcl.inline
 [dcl.link]: dcl.md#dcl.link
+[dcl.pre]: dcl.md#dcl.pre
 [definitions]: #definitions
 [depr]: future.md#depr
 [depr.c.headers]: future.md#depr.c.headers
 [derivation]: #derivation
 [derived.classes]: #derived.classes
 [description]: #description
 [diagnostics]: diagnostics.md#diagnostics
 [enumerated.types]: #enumerated.types
 [except]: except.md#except
+[except.spec]: except.md#except.spec
+[expos.only.func]: #expos.only.func
 [expos.only.types]: #expos.only.types
 [expr.cond]: expr.md#expr.cond
 [expr.const]: expr.md#expr.const
 [expr.delete]: expr.md#expr.delete
 [expr.eq]: expr.md#expr.eq
 [expr.new]: expr.md#expr.new
 [expr.rel]: expr.md#expr.rel
+[expr.spaceship]: expr.md#expr.spaceship
+[expr.unary.op]: expr.md#expr.unary.op
 [extern.names]: #extern.names
 [extern.types]: #extern.types
 [function.objects]: utilities.md#function.objects
 [functions.within.classes]: #functions.within.classes
 [global.functions]: #global.functions
 [handler.functions]: #handler.functions
 [hash.requirements]: #hash.requirements
 [headers]: #headers
+[headers.cpp]: #headers.cpp
+[headers.cpp.c]: #headers.cpp.c
+[headers.cpp.fs]: #headers.cpp.fs
+[hidden.friends]: #hidden.friends
 [input.output]: input.md#input.output
 [intro.compliance]: intro.md#intro.compliance
 [intro.defs]: intro.md#intro.defs
+[intro.execution]: basic.md#intro.execution
+[intro.multithread]: basic.md#intro.multithread
 [intro.refs]: intro.md#intro.refs
 [iterator.requirements]: iterators.md#iterator.requirements
 [iterators]: iterators.md#iterators
+[lex.name]: lex.md#lex.name
+[lex.name.special]: #lex.name.special
 [lex.phases]: lex.md#lex.phases
+[lex.separate]: lex.md#lex.separate
 [lib.types.movedfrom]: #lib.types.movedfrom
 [library]: #library
 [library.c]: #library.c
+[library.categories]: #library.categories
 [library.general]: #library.general
 [locales]: localization.md#locales
 [localization]: localization.md#localization
 [macro.names]: #macro.names
 [member.functions]: #member.functions
 [meta]: utilities.md#meta
+[module.import]: module.md#module.import
 [multibyte.strings]: #multibyte.strings
 [namespace.constraints]: #namespace.constraints
 [namespace.def]: dcl.md#namespace.def
 [namespace.future]: #namespace.future
 [namespace.posix]: #namespace.posix
 [namespace.std]: #namespace.std
 [namespace.udecl]: dcl.md#namespace.udecl
+[new.delete]: support.md#new.delete
+[new.handler]: support.md#new.handler
+[new.syn]: support.md#new.syn
 [nullablepointer.requirements]: #nullablepointer.requirements
 [numeric.requirements]: numerics.md#numeric.requirements
 [numerics]: numerics.md#numerics
 [objects.within.classes]: #objects.within.classes
 [organization]: #organization
 [over.literal]: over.md#over.literal
 [over.match]: over.md#over.match
 [over.oper]: over.md#over.oper
 [protection.within.classes]: #protection.within.classes
 [random.access.iterators]: iterators.md#random.access.iterators
+[ranges]: ranges.md#ranges
 [re]: re.md#re
 [reentrancy]: #reentrancy
 [replacement.functions]: #replacement.functions
 [requirements]: #requirements
 [res.on.arguments]: #res.on.arguments
 [res.on.data.races]: #res.on.data.races
 [res.on.exception.handling]: #res.on.exception.handling
+[res.on.expects]: #res.on.expects
 [res.on.functions]: #res.on.functions
 [res.on.headers]: #res.on.headers
 [res.on.macro.definitions]: #res.on.macro.definitions
 [res.on.objects]: #res.on.objects
 [res.on.pointer.storage]: #res.on.pointer.storage
+[res.on.requirements]: #res.on.requirements
 [reserved.names]: #reserved.names
+[specialized.addressof]: utilities.md#specialized.addressof
 [std.exceptions]: diagnostics.md#std.exceptions
+[stmt.return]: stmt.md#stmt.return
 [stream.types]: input.md#stream.types
 [strings]: strings.md#strings
 [structure]: #structure
 [structure.elements]: #structure.elements
 [structure.requirements]: #structure.requirements
 [structure.see.also]: #structure.see.also
 [structure.specifications]: #structure.specifications
 [structure.summary]: #structure.summary
+[support]: support.md#support
+[support.coroutine]: support.md#support.coroutine
+[support.dynamic]: support.md#support.dynamic
+[support.exception]: support.md#support.exception
+[support.initlist]: support.md#support.initlist
+[support.limits]: support.md#support.limits
+[support.rtti]: support.md#support.rtti
+[support.runtime]: support.md#support.runtime
+[support.srcloc]: support.md#support.srcloc
+[support.start.term]: support.md#support.start.term
+[support.types]: support.md#support.types
 [swappable.requirements]: #swappable.requirements
 [syserr]: diagnostics.md#syserr
 [syserr.errcode.overview]: diagnostics.md#syserr.errcode.overview
+[tab:allocator.req.var]: #tab:allocator.req.var
+[tab:cpp17.allocator]: #tab:cpp17.allocator
+[tab:cpp17.destructible]: #tab:cpp17.destructible
+[tab:cpp17.equalitycomparable]: #tab:cpp17.equalitycomparable
+[temp]: temp.md#temp
+[temp.concept]: temp.md#temp.concept
+[temp.constr.decl]: temp.md#temp.constr.decl
+[temp.constr.order]: temp.md#temp.constr.order
 [temp.deduct.call]: temp.md#temp.deduct.call
+[temp.func.order]: temp.md#temp.func.order
 [template.bitset]: utilities.md#template.bitset
+[terminate.handler]: support.md#terminate.handler
 [thread]: thread.md#thread
+[time]: time.md#time
 [type.descriptions]: #type.descriptions
 [type.descriptions.general]: #type.descriptions.general
 [using]: #using
 [using.headers]: #using.headers
 [using.linkage]: #using.linkage
 [using.overview]: #using.overview
 [usrlit.suffix]: #usrlit.suffix
 [utilities]: utilities.md#utilities
 [utility.arg.requirements]: #utility.arg.requirements
 [utility.requirements]: #utility.requirements
 [value.error.codes]: #value.error.codes
 [zombie.names]: #zombie.names
 [^3]: To save space, items that do not apply to a class are omitted. For
     example, if a class does not specify any comparison functions, there
     will be no “Comparison functions” subclause.
+[^4]: To save space, elements that do not apply to a function are
+ omitted. For example, if a function specifies no preconditions,
+    there will be no *Preconditions:* element.
 [^5]: This simplifies the presentation of complexity requirements in
     some cases.
 [^6]: Examples from  [[utility.requirements]] include:
+ *Cpp17EqualityComparable*, *Cpp17LessThanComparable*,
+ *Cpp17CopyConstructible*. Examples from  [[iterator.requirements]]
+ include: *Cpp17InputIterator*, *Cpp17ForwardIterator*.
+[^7]: Such as an integer type, with constant integer values
+    [[basic.fundamental]].
+[^8]: declared in `<clocale>`.
 [^9]: Many of the objects manipulated by function signatures declared in
+    `<cstring>` are character sequences or NTBSs. The size of some of
+    these character sequences is limited by a length value, maintained
+    separately from the character sequence.
+[^10]: A *string-literal*, such as `"abc"`, is a static NTBS.
 [^11]: An NTBS that contains characters only from the basic execution
     character set is also an NTMBS. Each multibyte character then
     consists of a single byte.
+[^12]: The C standard library headers [[depr.c.headers]] also define
+    names within the global namespace, while the C++ headers for C
+    library facilities [[headers]] may also define names within the
     global namespace.
 [^13]: This gives implementers freedom to use inline namespaces to
     support multiple configurations of the library.
 [^14]: A header is not necessarily a source file, nor are the sequences
     delimited by `<` and `>` in header names necessarily valid source
+    file names [[cpp.include]].
 [^15]: It is intentional that there is no C++ header for any of these C
     headers: `<stdatomic.h>`, `<stdnoreturn.h>`, `<threads.h>`.
 [^16]: This disallows the practice, allowed in C, of providing a masking
     macro in addition to the function prototype. The only way to achieve
     equivalent inline behavior in C++ is to provide a definition as an
     extern inline function.
+[^17]: In particular, including the standard header `<iso646.h>` has no
+    effect.
 [^18]: The `".h"` headers dump all their names into the global
     namespace, whereas the newer forms keep their names in namespace
     `std`. Therefore, the newer forms are the preferred forms for all
     uses except for C++ programs which are intended to be strictly
     from the C standard library is by including the header that declares
     it, notwithstanding the latitude granted in 7.1.4 of the C Standard.
 [^21]: Any library code that instantiates other library templates must
     be prepared to work adequately with any user-supplied specialization
+    that meets the minimum requirements of this document.
+[^22]: Any library customization point must be prepared to work
+    adequately with any user-defined overload that meets the minimum
+    requirements of this document. Therefore an implementation may
+    elect, under the as-if rule [[intro.execution]], to provide any
+    customization point in the form of an instantiated function object
+    [[function.objects]] even though the customization point’s
+    specification is in the form of a function template. The template
+    parameters of each such function object and the function parameters
+    and return type of the object’s `operator()` must match those of the
+    corresponding customization point’s specification.
+[^23]: The list of such reserved names includes `errno`, declared or
     defined in `<cerrno>`.
+[^24]: The list of such reserved function signatures with external
     linkage includes `setjmp(jmp_buf)`, declared or defined in
     `<csetjmp>`, and `va_end(va_list)`, declared or defined in
     `<cstdarg>`.
+[^25]: The function signatures declared in `<cuchar>`, `<cwchar>`, and
     `<cwctype>` are always reserved, notwithstanding the restrictions
     imposed in subclause 4.5.1 of Amendment 1 to the C Standard for
     these headers.
 [^26]: A valid C++ program always calls the expected library non-member
     function. An implementation may also define additional non-member
     functions that would otherwise not be called by a valid C++ program.
 [^27]: There is an implicit exception to this rule for types that are
+    described as synonyms for basic integral types, such as `size_t`
+    [[support.types]] and `streamoff` [[stream.types]].
 [^28]: That is, the C library functions can all be treated as if they
     are marked `noexcept`. This allows implementations to make
     performance optimizations based on the absence of exceptions at
     runtime.
+[^29]: The functions `qsort()` and `bsearch()` [[alg.c.library]] meet
     this condition.
 [^30]: In particular, they can report a failure to allocate storage by
     throwing an exception of type `bad_alloc`, or a class derived from
+    `bad_alloc` [[bad.alloc]].

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