`subview` doesn't seem to be documented

[pdimov]

I don't see it in https://www.boost.org/doc/libs/1_85_0/libs/static_string/doc/html/static_string/ref/boost__static_strings__basic_static_string.html.

[sdkrystian]

Seems like BOOST_STATIC_STRING_HAS_ANY_STRING_VIEW isn't being correctly set when running doxygen (the declaration of subview is guarded by #ifdef BOOST_STATIC_STRING_HAS_ANY_STRING_VIEW)? I think adding BOOST_STATIC_STRING_HAS_ANY_STRING_VIEW \\ here would fix it.

[vinniefalco]

One of the reasons I don't like "configuration macros" which effectively create two versions of the library.