FILENAME_MAX

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
version(none)
extern (C) nothrow @nogc
enum FILENAME_MAX = (!__traits(compiles, libressl_d.compat.stdio.FILENAME_MAX)) ? (core.sys.windows.windef.MAX_PATH) : (libressl_d.compat.stdio.FILENAME_MAX);

Meta