<!--external: When the EXPRESS schema is represented 'by-reference', the external XML attribute shall be present and its value shall identify a resource that contains the EXPRESS schema (text).-->
<!--schema_identifier: For an EXPRESS schema that is defined by a Part of ISO 10303 schema_identifier shall contain the ASN.1 (official identifier for a part of 10303 ) identifier value associated with that schema by that Part of ISO 10303-->
<!--Internal schema is not supported.--> </ex:express>