The INSTANCE# keyword determines whether certain requests will be processed with an instance number comparison. Instance number comparisons can be used to ensure that the expected instance of the note is being processed. If the creator of the note pad specified INSTCOMP=REQUIRED on the create note pad request, instance number comparisons are mandatory when writing, replacing, or deleting an existing note. Instance number comparisons are optional for read note requests.

If INSTANCE#=IGNORE is specified, or taken as the default, no instance number comparison is performed when processing the request.

Otherwise the INSTANCE# keyword identifies a storage area containing the instance number for the note. Depending on the request and its result, XCF might fetch an instance number from this storage area, or store an instance number in this storage area, or both. If the value fetched from the instance number storage area is zero, no instance number comparison is performed for the request.

• For a create note request, the IXCNOTE macro expansion stores the instance number of the note in the designated storage area upon return from the XCF Note Pad Services. The instance number is valid for use if the create request is either successful or rejected because the note already exists. Otherwise the stored instance number value is not valid for use (normally the stored value will be zero).
• For a write note request, the IXCNOTE macro expansion extracts the instance number from the designated storage area and calls the XCF Note Pad Services. If the designated note does not exist, the note is created and the instance number is set to a value determined by XCF. The specified input instance number is irrelevant and totally ignored in this case. If the designated note does exist, the note is replaced if the specified instance number is either zero or equal to the current instance number of the note (and the request is otherwise valid). Otherwise the request is rejected due to an instance number mismatch.

  Upon return from the XCF Note Pad Services, the IXCNOTE macro stores an instance number in the designated storage area. The instance number is valid for use if the write request was successful, or if the request was rejected due to either an instance number mismatch or a low tag value. Otherwise the instance number is not valid for use (normally the stored value will be the same as the original input value).

• For a read, replace, or delete request, the IXCNOTE macro expansion extracts the instance number from the designated storage area and calls the XCF Note Pad Services. If the designated note does not exist, the request is rejected. If the designated note does exist, the request is processed if the specified instance number is either zero or equal to the current instance number of the note (and the request is otherwise valid). Otherwise the request is rejected due to an instance number mismatch.

  Upon return from the XCF Note Pad Services, the IXCNOTE macro stores an instance number in the designated storage area. The instance number is valid for use if the request was successful, or if the request was rejected due to either an instance number mismatch or a low tag value. Otherwise the instance number is not valid for use (normally the stored value will be the same as the original input value).

Independently of the INSTANCE# specification, note that the metadata stored in the answer area (if any) includes the instance number for the note.