Specifies the type of ISIS callback being registered.

Values:

IG_SCANCB_BEFORE_PAGE	Specifies the callback function called before page transfer is initiated.
IG_SCANCB_AFTER_PAGE	Specifies the callback function called when page transfer is completed.
IG_SCANCB_AFTER_DOC	Specifies the callback function called when all document pages transfer is completed.
IG_SCANCB_CAP_SET_5	This value has been deprecated and will be removed from the public API in a future release.
IG_SCANCB_AFTER_PAGE_UI	This value has been deprecated and will be removed from the public API in a future release.