The identification information (typically the standard number, organization name, and title of the standard) for a cited standard, where “standard” is defined as a document produced by a recognized standards body such ISO, IEEE, OASIS, ANSI, etc.
<!ELEMENT std (#PCDATA %std-elements;)* >
Any combination of:
... <ref> <citation> <std>International standard ISO 10993-10:2002(E): Biological evaluation of medical devices-Part 10: Tests for irritation and delayed-type hypersensitivity</std>. <edition>Second</edition>. <year>2002</year>-<month>09</month>-<day>01</day> </citation> </ref> ...