[diff.cpp03] - C++20 → C++23

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@@ -1,16 +1,18 @@
 ## C++ and ISO C++03 <a id="diff.cpp03">[[diff.cpp03]]</a>
-This subclause lists the differences between C++ and ISO C++03 (ISO/IEC
-14882:2003, *Programming Languages — C++*), in addition to those listed
-above, by the chapters of this document.
 ###  [[lex]]: lexical conventions <a id="diff.cpp03.lex">[[diff.cpp03.lex]]</a>
 **Change:** New kinds of *string-literal*s. **Rationale:** Required for
 new features. **Effect on original feature:** Valid C++03 code may fail
-to compile or produce different results in this International Standard.
 Specifically, macros named `R`, `u8`, `u8R`, `u`, `uR`, `U`, `UR`, or
 `LR` will not be expanded when adjacent to a *string-literal* but will
 be interpreted as part of the *string-literal*. For example:
 ``` cpp
@@ -18,29 +20,29 @@ be interpreted as part of the *string-literal*. For example:
 const char* s = u8"def";        // Previously "abcdef", now "def"
 ```
 **Change:** User-defined literal string support. **Rationale:** Required
 for new features. **Effect on original feature:** Valid C++03 code may
-fail to compile or produce different results in this International
-Standard. For example:
 ``` cpp
 #define _x "there"
 "hello"_x           // #1
 ```
 Previously, \#1 would have consisted of two separate preprocessing
-tokens and the macro `_x` would have been expanded. In this
-International Standard, \#1 consists of a single preprocessing token, so
-the macro is not expanded.
 **Change:** New keywords. **Rationale:** Required for new features.
 **Effect on original feature:** Added to [[lex.key]], the following
 identifiers are new keywords: `alignas`, `alignof`, `char16_t`,
 `char32_t`, `constexpr`, `decltype`, `noexcept`, `nullptr`,
 `static_assert`, and `thread_local`. Valid C++03 code using these
-identifiers is invalid in this International Standard.
 **Change:** Type of integer literals. **Rationale:** C99 compatibility.
 **Effect on original feature:** Certain integer literals larger than can
 be represented by `long` could change from an unsigned integer type to
 `signed long long`.
@@ -48,12 +50,12 @@ be represented by `long` could change from an unsigned integer type to
 ###  [[expr]]: expressions <a id="diff.cpp03.expr">[[diff.cpp03.expr]]</a>
 **Change:** Only literals are integer null pointer constants.
 **Rationale:** Removing surprising interactions with templates and
 constant expressions. **Effect on original feature:** Valid C++03 code
-may fail to compile or produce different results in this International
-Standard. For example:
 ``` cpp
 void f(void *);     // #1
 void f(...);        // #2
 template<int N> void g() {
@@ -62,17 +64,17 @@ template<int N> void g() {
 ```
 **Change:** Specify rounding for results of integer `/` and `%`.
 **Rationale:** Increase portability, C99 compatibility. **Effect on
 original feature:** Valid C++03 code that uses integer division rounds
-the result toward 0 or toward negative infinity, whereas this
-International Standard always rounds the result toward 0.
 **Change:** `&&` is valid in a *type-name*. **Rationale:** Required for
 new features. **Effect on original feature:** Valid C++03 code may fail
-to compile or produce different results in this International Standard.
-For example:
 ``` cpp
 bool b1 = new int && false;             // previously false, now ill-formed
 struct S { operator int(); };
 bool b2 = &S::operator int && false;    // previously false, now ill-formed
@@ -81,24 +83,24 @@ bool b2 = &S::operator int && false;    // previously false, now ill-formed
 ###  [[dcl.dcl]]: declarations <a id="diff.cpp03.dcl.dcl">[[diff.cpp03.dcl.dcl]]</a>
 **Change:** Remove `auto` as a storage class specifier. **Rationale:**
 New feature. **Effect on original feature:** Valid C++03 code that uses
 the keyword `auto` as a storage class specifier may be invalid in this
-International Standard. In this International Standard, `auto` indicates
-that the type of a variable is to be deduced from its initializer
-expression.
 **Change:** Narrowing restrictions in aggregate initializers.
 **Rationale:** Catches bugs. **Effect on original feature:** Valid C++03
-code may fail to compile in this International Standard. For example,
-the following code is valid in C++03 but invalid in this International
-Standard because `double` to `int` is a narrowing conversion:
 ``` cpp
 int x[] = { 2.0 };
 ```
 ###  [[class]]: classes <a id="diff.cpp03.class">[[diff.cpp03.class]]</a>
 **Change:** Implicitly-declared special member functions are defined as
 deleted when the implicit definition would have been ill-formed.
 **Rationale:** Improves template argument deduction failure. **Effect on
@@ -108,139 +110,135 @@ member functions in a context where the definition is not required
 ill-formed.
 **Change:** User-declared destructors have an implicit exception
 specification. **Rationale:** Clarification of destructor requirements.
 **Effect on original feature:** Valid C++03 code may execute differently
-in this International Standard. In particular, destructors that throw
 exceptions will call `std::terminate` (without calling
 `std::unexpected`) if their exception specification is non-throwing.
 ###  [[temp]]: templates <a id="diff.cpp03.temp">[[diff.cpp03.temp]]</a>
-**Change:** Remove `export`. **Rationale:** No implementation consensus.
-**Effect on original feature:** A valid C++03 declaration containing
-`export` is ill-formed in this International Standard.
 **Change:** Remove whitespace requirement for nested closing template
 right angle brackets. **Rationale:** Considered a persistent but minor
 annoyance. Template aliases representing non-class types would
 exacerbate whitespace issues. **Effect on original feature:** Change to
 semantics of well-defined expression. A valid C++03 expression
 containing a right angle bracket (“`>`”) followed immediately by another
 right angle bracket may now be treated as closing two templates. For
-example, the following code is valid in C++03 because “`>>`” is a
-right-shift operator, but invalid in this International Standard because
-“`>>`” closes two templates.
 ``` cpp
 template <class T> struct X { };
 template <int N> struct Y { };
 X< Y< 1 >> 2 > > x;
 ```
 **Change:** Allow dependent calls of functions with internal linkage.
 **Rationale:** Overly constrained, simplify overload resolution rules.
-**Effect on original feature:** A valid C++03 program could get a
-different result than this International Standard.
 ###  [[library]]: library introduction <a id="diff.cpp03.library">[[diff.cpp03.library]]</a>
 **Affected:** [[library]] – [[thread]] **Change:** New reserved
 identifiers. **Rationale:** Required by new features. **Effect on
 original feature:** Valid C++03 code that uses any identifiers added to
-the C++ standard library by this International Standard may fail to
-compile or produce different results in this International Standard. A
-comprehensive list of identifiers used by the C++ standard library can
-be found in the Index of Library Names in this International Standard.
 **Change:** New headers. **Rationale:** New functionality. **Effect on
 original feature:** The following C++ headers are new: `<array>`,
 `<atomic>`, `<chrono>`, , `<condition_variable>`, `<forward_list>`,
 `<future>`, `<initializer_list>`, `<mutex>`, `<random>`, `<ratio>`,
 `<regex>`, `<scoped_allocator>`, `<system_error>`, `<thread>`,
 `<tuple>`, `<typeindex>`, `<type_traits>`, `<unordered_map>`, and
 `<unordered_set>`. In addition the following C compatibility headers are
 new: `<cfenv>`, `<cinttypes>`, `<cstdint>`, and `<cuchar>`. Valid C++03
 code that `#include`s headers with these names may be invalid in this
-International Standard.
 **Effect on original feature:** Function `swap` moved to a different
 header **Rationale:** Remove dependency on `<algorithm>` for `swap`.
 **Effect on original feature:** Valid C++03 code that has been compiled
 expecting swap to be in `<algorithm>` may have to instead include
 `<utility>`.
 **Change:** New reserved namespace. **Rationale:** New functionality.
 **Effect on original feature:** The global namespace `posix` is now
 reserved for standardization. Valid C++03 code that uses a top-level
-namespace `posix` may be invalid in this International Standard.
 **Change:** Additional restrictions on macro names. **Rationale:** Avoid
 hard to diagnose or non-portable constructs. **Effect on original
 feature:** Names of attribute identifiers may not be used as macro
 names. Valid C++03 code that defines `override`, `final`,
 `carries_dependency`, or `noreturn` as macros is invalid in this
-International Standard.
 ###  [[support]]: language support library <a id="diff.cpp03.language.support">[[diff.cpp03.language.support]]</a>
 **Change:** `operator new` may throw exceptions other than
 `std::bad_alloc`. **Rationale:** Consistent application of `noexcept`.
 **Effect on original feature:** Valid C++03 code that assumes that
 global `operator new` only throws `std::bad_alloc` may execute
-differently in this International Standard. Valid C++03 code that
-replaces the global replaceable `operator new` is ill-formed in this
-International Standard, because the exception specification of
-`throw(std::bad_alloc)` was removed.
 ###  [[diagnostics]]: diagnostics library <a id="diff.cpp03.diagnostics">[[diff.cpp03.diagnostics]]</a>
 **Change:** Thread-local error numbers. **Rationale:** Support for new
 thread facilities. **Effect on original feature:** Valid but
 implementation-specific C++03 code that relies on `errno` being the same
-across threads may change behavior in this International Standard.
 ###  [[utilities]]: general utilities library <a id="diff.cpp03.utilities">[[diff.cpp03.utilities]]</a>
-**Change:** Minimal support for garbage-collected regions.
-**Rationale:** Required by new feature. **Effect on original feature:**
-Valid C++03 code, compiled without traceable pointer support, that
-interacts with newer C++ code using regions declared reachable may have
-different runtime behavior.
 **Change:** Standard function object types no longer derived from
 `std::unary_function` or `std::binary_function`. **Rationale:**
 Superseded by new feature; `unary_function` and `binary_function` are no
 longer defined. **Effect on original feature:** Valid C++03 code that
 depends on function object types being derived from `unary_function` or
-`binary_function` may fail to compile in this International Standard.
 ###  [[strings]]: strings library <a id="diff.cpp03.strings">[[diff.cpp03.strings]]</a>
 **Change:** `basic_string` requirements no longer allow
 reference-counted strings. **Rationale:** Invalidation is subtly
 different with reference-counted strings. This change regularizes
-behavior for this International Standard. **Effect on original
-feature:** Valid C++03 code may execute differently in this
-International Standard.
 **Change:** Loosen `basic_string` invalidation rules. **Rationale:**
 Allow small-string optimization. **Effect on original feature:** Valid
-C++03 code may execute differently in this International Standard. Some
-`const` member functions, such as `data` and `c_str`, no longer
-invalidate iterators.
 ###  [[containers]]: containers library <a id="diff.cpp03.containers">[[diff.cpp03.containers]]</a>
 **Change:** Complexity of `size()` member functions now constant.
 **Rationale:** Lack of specification of complexity of `size()` resulted
 in divergent implementations with inconsistent performance
 characteristics. **Effect on original feature:** Some container
 implementations that conform to C++03 may not conform to the specified
-`size()` requirements in this International Standard. Adjusting
-containers such as `std::list` to the stricter requirements may require
-incompatible changes.
 **Change:** Requirements change: relaxation. **Rationale:**
 Clarification. **Effect on original feature:** Valid C++03 code that
 attempts to meet the specified container requirements may now be
 over-specified. Code that attempted to be portable across containers may
@@ -267,11 +265,11 @@ functions have changed:
 - `insert(pos, num, val)` for `vector`, `deque`, `list`, `forward_list`
 - `insert(pos, beg, end)` for `vector`, `deque`, `list`, `forward_list`
 Valid C++03 code that relies on these functions returning `void` (e.g.,
 code that creates a pointer to member function that points to one of
-these functions) will fail to compile with this International Standard.
 **Change:** Signature changes: from `iterator` to `const_iterator`
 parameters. **Rationale:** Overspecification. **Effect on original
 feature:** The signatures of the following member functions changed from
 taking an `iterator` to taking a `const_iterator`:
@@ -282,44 +280,51 @@ taking an `iterator` to taking a `const_iterator`:
 - `erase(begin, end)` for `set`, `multiset`, `map`, `multimap`
 - all forms of `list::splice`
 - all forms of `list::merge`
 Valid C++03 code that uses these functions may fail to compile with this
-International Standard.
 **Change:** Signature changes: `resize`. **Rationale:** Performance,
 compatibility with move semantics. **Effect on original feature:** For
 `vector`, `deque`, and `list` the fill value passed to `resize` is now
 passed by reference instead of by value, and an additional overload of
 `resize` has been added. Valid C++03 code that uses this function may
-fail to compile with this International Standard.
 ###  [[algorithms]]: algorithms library <a id="diff.cpp03.algorithms">[[diff.cpp03.algorithms]]</a>
 **Change:** Result state of inputs after application of some algorithms.
 **Rationale:** Required by new feature. **Effect on original feature:**
 A valid C++03 program may detect that an object with a valid but
 unspecified state has a different valid but unspecified state with this
-International Standard. For example, `std::remove` and `std::remove_if`
-may leave the tail of the input sequence with a different set of values
-than previously.
 ###  [[numerics]]: numerics library <a id="diff.cpp03.numerics">[[diff.cpp03.numerics]]</a>
 **Change:** Specified representation of complex numbers. **Rationale:**
 Compatibility with C99. **Effect on original feature:** Valid C++03 code
 that uses implementation-specific knowledge about the binary
 representation of the required template specializations of
-`std::complex` may not be compatible with this International Standard.
 ###  [[input.output]]: input/output library <a id="diff.cpp03.input.output">[[diff.cpp03.input.output]]</a>
 **Change:** Specify use of `explicit` in existing boolean conversion
 functions. **Rationale:** Clarify intentions, avoid workarounds.
 **Effect on original feature:** Valid C++03 code that relies on implicit
-boolean conversions will fail to compile with this International
-Standard. Such conversions occur in the following conditions:
 - passing a value to a function that takes an argument of type `bool`;
 - using `operator==` to compare to `false` or `true`;
 - returning a value from a function with a return type of `bool`;
 - initializing members of type `bool` via aggregate initialization;
@@ -329,18 +334,18 @@ Standard. Such conversions occur in the following conditions:
 **Rationale:** More detailed error messages. **Effect on original
 feature:** `std::ios_base::failure` is no longer derived directly from
 `std::exception`, but is now derived from `std::system_error`, which in
 turn is derived from `std::runtime_error`. Valid C++03 code that assumes
 that `std::ios_base::failure` is derived directly from `std::exception`
-may execute differently in this International Standard.
 **Change:** Flag types in `std::ios_base` are now bitmasks with values
 defined as constexpr static members. **Rationale:** Required for new
 features. **Effect on original feature:** Valid C++03 code that relies
 on `std::ios_base` flag types being represented as `std::bitset` or as
-an integer type may fail to compile with this International Standard.
-For example:
 ``` cpp
 #include <iostream>
 int main() {

 ## C++ and ISO C++03 <a id="diff.cpp03">[[diff.cpp03]]</a>
+### General <a id="diff.cpp03.general">[[diff.cpp03.general]]</a>
+Subclause [[diff.cpp03]] lists the differences between C++ and ISO C++03
+(ISO/IEC 14882:2003, *Programming Languages — C++*), in addition to
+those listed above, by the chapters of this document.
 ###  [[lex]]: lexical conventions <a id="diff.cpp03.lex">[[diff.cpp03.lex]]</a>
 **Change:** New kinds of *string-literal*s. **Rationale:** Required for
 new features. **Effect on original feature:** Valid C++03 code may fail
+to compile or produce different results in this revision of C++.
 Specifically, macros named `R`, `u8`, `u8R`, `u`, `uR`, `U`, `UR`, or
 `LR` will not be expanded when adjacent to a *string-literal* but will
 be interpreted as part of the *string-literal*. For example:
 ``` cpp
 const char* s = u8"def";        // Previously "abcdef", now "def"
 ```
 **Change:** User-defined literal string support. **Rationale:** Required
 for new features. **Effect on original feature:** Valid C++03 code may
+fail to compile or produce different results in this revision of C++.
+For example:
 ``` cpp
 #define _x "there"
 "hello"_x           // #1
 ```
 Previously, \#1 would have consisted of two separate preprocessing
+tokens and the macro `_x` would have been expanded. In this revision of
+C++, \#1 consists of a single preprocessing token, so the macro is not
+expanded.
 **Change:** New keywords. **Rationale:** Required for new features.
 **Effect on original feature:** Added to [[lex.key]], the following
 identifiers are new keywords: `alignas`, `alignof`, `char16_t`,
 `char32_t`, `constexpr`, `decltype`, `noexcept`, `nullptr`,
 `static_assert`, and `thread_local`. Valid C++03 code using these
+identifiers is invalid in this revision of C++.
 **Change:** Type of integer literals. **Rationale:** C99 compatibility.
 **Effect on original feature:** Certain integer literals larger than can
 be represented by `long` could change from an unsigned integer type to
 `signed long long`.
 ###  [[expr]]: expressions <a id="diff.cpp03.expr">[[diff.cpp03.expr]]</a>
 **Change:** Only literals are integer null pointer constants.
 **Rationale:** Removing surprising interactions with templates and
 constant expressions. **Effect on original feature:** Valid C++03 code
+may fail to compile or produce different results in this revision of
+C++. For example:
 ``` cpp
 void f(void *);     // #1
 void f(...);        // #2
 template<int N> void g() {
 ```
 **Change:** Specify rounding for results of integer `/` and `%`.
 **Rationale:** Increase portability, C99 compatibility. **Effect on
 original feature:** Valid C++03 code that uses integer division rounds
+the result toward 0 or toward negative infinity, whereas this revision
+of C++ always rounds the result toward 0.
 **Change:** `&&` is valid in a *type-name*. **Rationale:** Required for
 new features. **Effect on original feature:** Valid C++03 code may fail
+to compile or produce different results in this revision of C++. For
+example:
 ``` cpp
 bool b1 = new int && false;             // previously false, now ill-formed
 struct S { operator int(); };
 bool b2 = &S::operator int && false;    // previously false, now ill-formed
 ###  [[dcl.dcl]]: declarations <a id="diff.cpp03.dcl.dcl">[[diff.cpp03.dcl.dcl]]</a>
 **Change:** Remove `auto` as a storage class specifier. **Rationale:**
 New feature. **Effect on original feature:** Valid C++03 code that uses
 the keyword `auto` as a storage class specifier may be invalid in this
+revision of C++. In this revision of C++, `auto` indicates that the type
+of a variable is to be deduced from its initializer expression.
 **Change:** Narrowing restrictions in aggregate initializers.
 **Rationale:** Catches bugs. **Effect on original feature:** Valid C++03
+code may fail to compile in this revision of C++. For example:
 ``` cpp
 int x[] = { 2.0 };
 ```
+This code is valid in C++03 but invalid in this revision of C++ because
+`double` to `int` is a narrowing conversion.
 ###  [[class]]: classes <a id="diff.cpp03.class">[[diff.cpp03.class]]</a>
 **Change:** Implicitly-declared special member functions are defined as
 deleted when the implicit definition would have been ill-formed.
 **Rationale:** Improves template argument deduction failure. **Effect on
 ill-formed.
 **Change:** User-declared destructors have an implicit exception
 specification. **Rationale:** Clarification of destructor requirements.
 **Effect on original feature:** Valid C++03 code may execute differently
+in this revision of C++. In particular, destructors that throw
 exceptions will call `std::terminate` (without calling
 `std::unexpected`) if their exception specification is non-throwing.
 ###  [[temp]]: templates <a id="diff.cpp03.temp">[[diff.cpp03.temp]]</a>
+**Change:** Repurpose `export` for modules
+[[module]], [[cpp.module]], [[cpp.import]]. **Rationale:** No
+implementation consensus for the C++03 meaning of `export`. **Effect on
+original feature:** A valid C++03 program containing `export` is
+ill-formed in this revision of C++.
 **Change:** Remove whitespace requirement for nested closing template
 right angle brackets. **Rationale:** Considered a persistent but minor
 annoyance. Template aliases representing non-class types would
 exacerbate whitespace issues. **Effect on original feature:** Change to
 semantics of well-defined expression. A valid C++03 expression
 containing a right angle bracket (“`>`”) followed immediately by another
 right angle bracket may now be treated as closing two templates. For
+example:
 ``` cpp
 template <class T> struct X { };
 template <int N> struct Y { };
 X< Y< 1 >> 2 > > x;
 ```
+This code is valid in C++03 because “`>>`” is a right-shift operator,
+but invalid in this revision of C++ because “`>>`” closes two templates.
 **Change:** Allow dependent calls of functions with internal linkage.
 **Rationale:** Overly constrained, simplify overload resolution rules.
+**Effect on original feature:** A valid C++03 program can get a
+different result in this revision of C++.
 ###  [[library]]: library introduction <a id="diff.cpp03.library">[[diff.cpp03.library]]</a>
 **Affected:** [[library]] – [[thread]] **Change:** New reserved
 identifiers. **Rationale:** Required by new features. **Effect on
 original feature:** Valid C++03 code that uses any identifiers added to
+the C++ standard library by later revisions of C++ may fail to compile
+or produce different results in this revision of C++. A comprehensive
+list of identifiers used by the C++ standard library can be found in the
+Index of Library Names in this document.
 **Change:** New headers. **Rationale:** New functionality. **Effect on
 original feature:** The following C++ headers are new: `<array>`,
 `<atomic>`, `<chrono>`, , `<condition_variable>`, `<forward_list>`,
 `<future>`, `<initializer_list>`, `<mutex>`, `<random>`, `<ratio>`,
 `<regex>`, `<scoped_allocator>`, `<system_error>`, `<thread>`,
 `<tuple>`, `<typeindex>`, `<type_traits>`, `<unordered_map>`, and
 `<unordered_set>`. In addition the following C compatibility headers are
 new: `<cfenv>`, `<cinttypes>`, `<cstdint>`, and `<cuchar>`. Valid C++03
 code that `#include`s headers with these names may be invalid in this
+revision of C++.
 **Effect on original feature:** Function `swap` moved to a different
 header **Rationale:** Remove dependency on `<algorithm>` for `swap`.
 **Effect on original feature:** Valid C++03 code that has been compiled
 expecting swap to be in `<algorithm>` may have to instead include
 `<utility>`.
 **Change:** New reserved namespace. **Rationale:** New functionality.
 **Effect on original feature:** The global namespace `posix` is now
 reserved for standardization. Valid C++03 code that uses a top-level
+namespace `posix` may be invalid in this revision of C++.
 **Change:** Additional restrictions on macro names. **Rationale:** Avoid
 hard to diagnose or non-portable constructs. **Effect on original
 feature:** Names of attribute identifiers may not be used as macro
 names. Valid C++03 code that defines `override`, `final`,
 `carries_dependency`, or `noreturn` as macros is invalid in this
+revision of C++.
 ###  [[support]]: language support library <a id="diff.cpp03.language.support">[[diff.cpp03.language.support]]</a>
 **Change:** `operator new` may throw exceptions other than
 `std::bad_alloc`. **Rationale:** Consistent application of `noexcept`.
 **Effect on original feature:** Valid C++03 code that assumes that
 global `operator new` only throws `std::bad_alloc` may execute
+differently in this revision of C++. Valid C++03 code that replaces the
+global replaceable `operator new` is ill-formed in this revision of C++,
+because the exception specification of `throw(std::bad_alloc)` was
+removed.
 ###  [[diagnostics]]: diagnostics library <a id="diff.cpp03.diagnostics">[[diff.cpp03.diagnostics]]</a>
 **Change:** Thread-local error numbers. **Rationale:** Support for new
 thread facilities. **Effect on original feature:** Valid but
 implementation-specific C++03 code that relies on `errno` being the same
+across threads may change behavior in this revision of C++.
 ###  [[utilities]]: general utilities library <a id="diff.cpp03.utilities">[[diff.cpp03.utilities]]</a>
 **Change:** Standard function object types no longer derived from
 `std::unary_function` or `std::binary_function`. **Rationale:**
 Superseded by new feature; `unary_function` and `binary_function` are no
 longer defined. **Effect on original feature:** Valid C++03 code that
 depends on function object types being derived from `unary_function` or
+`binary_function` may fail to compile in this revision of C++.
 ###  [[strings]]: strings library <a id="diff.cpp03.strings">[[diff.cpp03.strings]]</a>
 **Change:** `basic_string` requirements no longer allow
 reference-counted strings. **Rationale:** Invalidation is subtly
 different with reference-counted strings. This change regularizes
+behavior. **Effect on original feature:** Valid C++03 code may execute
+differently in this revision of C++.
 **Change:** Loosen `basic_string` invalidation rules. **Rationale:**
 Allow small-string optimization. **Effect on original feature:** Valid
+C++03 code may execute differently in this revision of C++. Some `const`
+member functions, such as `data` and `c_str`, no longer invalidate
+iterators.
 ###  [[containers]]: containers library <a id="diff.cpp03.containers">[[diff.cpp03.containers]]</a>
 **Change:** Complexity of `size()` member functions now constant.
 **Rationale:** Lack of specification of complexity of `size()` resulted
 in divergent implementations with inconsistent performance
 characteristics. **Effect on original feature:** Some container
 implementations that conform to C++03 may not conform to the specified
+`size()` requirements in this revision of C++. Adjusting containers such
+as `std::list` to the stricter requirements may require incompatible
+changes.
 **Change:** Requirements change: relaxation. **Rationale:**
 Clarification. **Effect on original feature:** Valid C++03 code that
 attempts to meet the specified container requirements may now be
 over-specified. Code that attempted to be portable across containers may
 - `insert(pos, num, val)` for `vector`, `deque`, `list`, `forward_list`
 - `insert(pos, beg, end)` for `vector`, `deque`, `list`, `forward_list`
 Valid C++03 code that relies on these functions returning `void` (e.g.,
 code that creates a pointer to member function that points to one of
+these functions) will fail to compile with this revision of C++.
 **Change:** Signature changes: from `iterator` to `const_iterator`
 parameters. **Rationale:** Overspecification. **Effect on original
 feature:** The signatures of the following member functions changed from
 taking an `iterator` to taking a `const_iterator`:
 - `erase(begin, end)` for `set`, `multiset`, `map`, `multimap`
 - all forms of `list::splice`
 - all forms of `list::merge`
 Valid C++03 code that uses these functions may fail to compile with this
+revision of C++.
 **Change:** Signature changes: `resize`. **Rationale:** Performance,
 compatibility with move semantics. **Effect on original feature:** For
 `vector`, `deque`, and `list` the fill value passed to `resize` is now
 passed by reference instead of by value, and an additional overload of
 `resize` has been added. Valid C++03 code that uses this function may
+fail to compile with this revision of C++.
 ###  [[algorithms]]: algorithms library <a id="diff.cpp03.algorithms">[[diff.cpp03.algorithms]]</a>
 **Change:** Result state of inputs after application of some algorithms.
 **Rationale:** Required by new feature. **Effect on original feature:**
 A valid C++03 program may detect that an object with a valid but
 unspecified state has a different valid but unspecified state with this
+revision of C++. For example, `std::remove` and `std::remove_if` may
+leave the tail of the input sequence with a different set of values than
+previously.
 ###  [[numerics]]: numerics library <a id="diff.cpp03.numerics">[[diff.cpp03.numerics]]</a>
 **Change:** Specified representation of complex numbers. **Rationale:**
 Compatibility with C99. **Effect on original feature:** Valid C++03 code
 that uses implementation-specific knowledge about the binary
 representation of the required template specializations of
+`std::complex` may not be compatible with this revision of C++.
+###  [[localization]]: localization library <a id="diff.cpp03.locale">[[diff.cpp03.locale]]</a>
+**Change:** The `num_get` facet recognizes hexadecimal floating point
+values. **Rationale:** Required by new feature. **Effect on original
+feature:** Valid C++03 code may have different behavior in this revision
+of C++.
 ###  [[input.output]]: input/output library <a id="diff.cpp03.input.output">[[diff.cpp03.input.output]]</a>
 **Change:** Specify use of `explicit` in existing boolean conversion
 functions. **Rationale:** Clarify intentions, avoid workarounds.
 **Effect on original feature:** Valid C++03 code that relies on implicit
+boolean conversions will fail to compile with this revision of C++. Such
+conversions occur in the following conditions:
 - passing a value to a function that takes an argument of type `bool`;
 - using `operator==` to compare to `false` or `true`;
 - returning a value from a function with a return type of `bool`;
 - initializing members of type `bool` via aggregate initialization;
 **Rationale:** More detailed error messages. **Effect on original
 feature:** `std::ios_base::failure` is no longer derived directly from
 `std::exception`, but is now derived from `std::system_error`, which in
 turn is derived from `std::runtime_error`. Valid C++03 code that assumes
 that `std::ios_base::failure` is derived directly from `std::exception`
+may execute differently in this revision of C++.
 **Change:** Flag types in `std::ios_base` are now bitmasks with values
 defined as constexpr static members. **Rationale:** Required for new
 features. **Effect on original feature:** Valid C++03 code that relies
 on `std::ios_base` flag types being represented as `std::bitset` or as
+an integer type may fail to compile with this revision of C++. For
+example:
 ``` cpp
 #include <iostream>
 int main() {

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