User-written checking is performed through LPFNIG_REC_WORD_CHECK user-written callback function by the integrating application. When creating or updating a zone, the CheckWordCB field of the zone may contain the address of such a function. During recognition, when it is called, the user-written function is passed the string to be checked and the index of the zone (from which the string to be checked is derived). The user-written function should evaluate the string, knowing the pattern of permissible zone content. Its opinion on the recognized string's acceptability should be expressed with one of the five values from the enumIGRecCheckWordReturnCode enumeration.