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All library entities except operator new and operator delete are defined within the namespace std or namespaces nested within namespace std.134

It is unspecified whether names declared in a specific namespace are declared directly in that namespace or in an inline namespace inside that namespace.135

Whenever an unqualified name other than swap, make_error_code, make_error_condition, from_stream, or submdspan_mapping is used in the specification of a declaration D in [support] through [exec] or [depr], its meaning is established as-if by performing unqualified name lookup ([basic.lookup.unqual]) in the context of D.

[Note 1:

Argument-dependent lookup is not performed.

— end note]

Similarly, the meaning of a qualified-id is established as-if by performing qualified name lookup ([basic.lookup.qual]) in the context of D.

[Example 1:

The reference to is_array_v in the specification of std::to_array ([array.creation]) refers to ::std::is_array_v.

— end example]

[Note 2:

Operators in expressions ([over.match.oper]) are not so constrained; see [global.functions].

— end note]

The meaning of the unqualified name swap is established in an overload resolution context for swappable values ([swappable.requirements]).

The meanings of the unqualified names make_error_code, make_error_condition, from_stream, and submdspan_mapping are established as-if by performing argument-dependent lookup ([basic.lookup.argdep]).

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The C standard library headers ([support.c.headers]) also define names within the global namespace, while the C++ headers for C library facilities ([headers]) can also define names within the global namespace.

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This gives implementers freedom to use inline namespaces to support multiple configurations of the library.