s the child
     options to be grouped together; to achieve this effect without actually
     printing a header string, use a value of "".  */
  const char *header;

  /* Where to group the child options relative to the other (`consolidated')
     options in the parent argp; the values are the same as the GROUP field
     in argp_option structs, but all child-groupings follow parent options at
     a particular group level.  If both this field and HEADER are zero, then
     they aren't grouped at all, but rather merged with the parent options
     (merging the child's grouping levels with the parents).  */
  int group;
};