ever their intended role.
It is the authors view that the majority of custom argument checking
tasks are better done as a second stage in your program after
argtable has done its job. It is usually much simpler to implement
additional post-parse checks in your own code than creating custom
argtable callbacks that do it all. Custom callbacks are really only
required if you are scanning data types that argtable does not
support natively. In such cases you may also need to create a custom
arg_xxx structure in 