If the arg-type is keyword (see Arg Type Keyword) or
set-membership (see Arg Type Set Membership), then you must specify
the list of keywords by a series of keyword entries. The interface
file will contain values for <OPTN_NAME>_<KEYWORD> for each
keyword entry. keyword option types will have an enumeration and
set-membership option types will have a set of unsigned bits
#define-d.
If the arg-type is specifically keyword, you may also add
special handling code with a
extra-code attribute. After optionEnumerationVal has
converted the input string into an enumeration, you may insert code to
process this enumeration value (pOptDesc->optArg.argEnum).