[xpressive] Where are the names in the c_ctype.h file coming from
In the xpressive header file c_ctype.h there are names such as _ALPHA,
_UPPER, _LOWER, _DIGIT etc. Where are these names declared or defined ?
I searched through all the Boost libraries and did not find any of these
names declared or defined anywhere. Are they supposed to be part of some
C++ standard header file ?