The following special values may be passed to an argp help filter function as the first argument in addition to key values for user options. They specify which help text the text argument contains:
ARGP_KEY_HELP_PRE_DOCARGP_KEY_HELP_POST_DOCARGP_KEY_HELP_HEADERARGP_KEY_HELP_EXTRAARGP_KEY_HELP_DUP_ARGS_NOTEARGP_KEY_HELP_ARGS_DOCargs_doc field from the argp parser. See Argp Parsers.