an_id	IN:	AN interface identifier returned by ANstart
	ann_tag	IN:	Tag of the annotation
	ann_ref	IN:	Reference number of the annotation

	Purpose	Returns the identifier of an annotation given its tag/reference number pair.
	Return value	Returns the annotation identifier (ann_id) if successful and FAIL (or -1) otherwise.
	Description	ANtagref2id returns the identifier of the annotation specified by its tag, ann_tag, and its reference number, ann_ref.
		Valid values of ann_tag are DFTAG_DIL (or 104) for a data label, DFTAG_DIA (or 105) for a data description, DFTAG_FID (or 100) for a file label, and DFTAG_FD (or 101) for a file description.

	FORTRAN	integer function aftagrefid(an_id, ann_tag, ann_ref)
		integer an_id, ann_tag, ann_ref