Several places in this document make unqualified calls to buffer_size. The context in which these calls are evaluated shall ensure that a unary non-member function named buffer_size is selected via overload resolution (C++ 2014 [over.match]) on a candidate set that includes:
the buffer_size function template defined in <experimental/buffer> ([buffer.synop]) and
the lookup set produced by argument-dependent lookup (C++ 2014 [basic.lookup.argdep]).