Synopsis:
   $igetmatches(<array> <pattern>)
   $igetrmatches(<array> <string>)

Technical:
   This functions operate in a manner similar to $getmatches() and
   $getrmatches(), except that they return an index number (in alphabetical
   order) of the array members rather than the item numbers.

Returns:
   space-separated list of array index numbers corresponding to matches

See Also:
   Arrays(7); matchitem(6); rmatchitem(6); getmatches(6);
   getrmatches(6); gettmatch(6)