This function returns the OID of the last element within the text or file entity specified by OID oid. This function returns the null OID if oid is not a file or text entity or if there are no elements within the entity. If oid is a file entity reference, the OID returned is in a different document tree than the one oid is in. If oid is a text entity, the OID returned would be in the same document as the one oid is in.