Included in content model of elements (1):

May contain elements by substitutions (122):

abbrev, acronym, action, application, author, authorinitials, bibliolist, biblioref, calloutlist, caution, citation, citerefentry, citetitle, classname, classsynopsis, cmdsynopsis, code, command, computeroutput, constant, constructorsynopsis, corpauthor, corpcredit, database, destructorsynopsis, email, emphasis, envar, errorcode, errorname, errortext, errortype, exceptionname, fieldsynopsis, filename, firstterm, footnote, footnoteref, foreignphrase, formalpara, funcsynopsis, function, glosslist, glossterm, guibutton, guiicon, guilabel, guimenu, guimenuitem, guisubmenu, hardware, important, indexterm, inlineequation, inlinegraphic, inlinemediaobject, interface, interfacename, itemizedlist, keycap, keycode, keycombo, keysym, link, literal, literallayout, markup, medialabel, menuchoice, methodname, methodsynopsis, modespec, mousebutton, note, olink, ooclass, ooexception, oointerface, option, optional, orderedlist, orgname, othercredit, package, para, parameter, personname, phrase, productname, productnumber, programlisting, programlistingco, prompt, property, quote, replaceable, returnvalue, revhistory, screen, screenco, screenshot, segmentedlist, sgmltag, simpara, simplelist, structfield, structname, symbol, synopsis, systemitem, tip, token, trademark, type, ulink, uri, userinput, variablelist, varname, warning, wordasword, xref

In anonymous complexTypes of elements (1):

tr [ref]