Return a reference to a character set.
Defined in header
template< class CharSet> constexpr implementation-defined ref( CharSet const& cs);
This function returns a character set which references the specified object.
This is used to reduce the number of bytes of storage (
required by a combinator when it stores a copy of the object.
Ownership of the object is not transferred; the caller is responsible for
ensuring the lifetime of the object is extended until it is no longer referenced.
For best results,
only be used with compile-time constants.