E="margin-top: 0.51cm; margin-bottom: 0.51cm">This topic shows
how to write your own argtable callback functions for controlling the
parsing, validation, and error reporting aspects of the command line
parsing. Each <I>arg_xxx</I> struct has four callback routines that
get called by the argtable parser. These are buried within the
<I>arg_hdr</I> structure that each <I>arg_xxx</I> structure has.
Among other things, you can see the relevant function pointers below.
They are called <I>resetfn</I>, <I>scanfn</I