allowable yes response - a locale-dependent affirmative response determined by the value of YESSTR.

allowable no response - a locale-dependent negative response determined by the value of NOSTR.

YESSTR - nl_langinfo item which causes nl_langinfo to return a pointer to an extended regular expression which describes allowable yes responses.

NOSTR - nl_langinfo item which causes nl_langinfo to return a pointer to an extended regular expression which describes allowable no responses.

There is no standard function which determines whether a given response is an allowable yes response, an allowable no response, or neither. In AIX, the rpmatch() function will do this.