[1] Open Publication Structure (OPS) 2.0.1 v1.0 (2015-09-08 04:50:12 +09:00 版) <http://www.idpf.org/epub/20/spec/OPS_2.0_latest.htm#Section1.3.7>
application/x-dtbook+xml http://www.niso.org/standards/resources/Z39-86-2005.html Used for OPS Content Documents