Object Identifier Attributes parameter entity see %object-id-atts;
object type see @object-id-type
On Behalf of Content Elements parameter entity see %on-behalf-of-elements;
online date see @date-type
online location identifier see <elocation-id>
online version see <self-uri>
ontology see @kwd-group-type
op cit see Abbreviated Citations
open access see <license>
open access fee information see <funding-group>
Open Access Model parameter entity see %open-access-model;
ORCID see <contrib-id> see @contrib-id-type
order see <named-content>
ordered see @list-type
ordered list see <list>
ordinals in citations see Tagging Ordinal Numbers
Ordinary Symbols for MathML parameter entity see %ISOamso;
organization see <aff>
organizational address see <address>
organizational author see <collab>
organization name see <collab> see <institution>
origination see <source>
other information, concerning an author see <author-comment>
outline see <abstract>
outside flow see <boxed-text>
owner, copyright use <copyright-holder>