16 Library introduction [library]

16.4 Library-wide requirements [requirements]

16.4.6 Conforming implementations [conforming]

16.4.6.4 Non-member functions [global.functions]

1
#
It is unspecified whether any non-member functions in the C++ standard library are defined as inline.
2
#
A call to a non-member function signature described in [support] through [exec] and [depr] shall behave as if the implementation declared no additional non-member function signatures.145
3
#
An implementation shall not declare a non-member function signature with additional default arguments.
4
#
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]) where lookup for the expression *out_stream << value includes the associated namespaces of value's type.
— end note]
145)145)
A valid C++ program always calls the expected library non-member function.
An implementation can also define additional non-member functions that would otherwise not be called by a valid C++ program.