Two modifiers to the structured comments indicate special
behavior of the function. The modifiers must come after the character that
indicates a routine, macro, or documentation.
The modifier C indicates that this routine is available only in C (and
not from Fortran). For example, the Swap program cannot be used in
Fortran, so its structured comment should be
/*@C .... @*/The modifier X indicates that the routine requires the X11 Window System. This is intended primarily for the program bfort [(ref bfort)], which is used to generate Fortran interfaces for systems that do not have X11.
The modifiers C and X may be used together and may be specified in either order (i.e., CX or XC).