See indexterm (db.indexterm.singular).

It is possible to construct index terms that are difficult to parse at best and totally illogical at worst. Consider the following:

<indexterm class='startofrange' zone="id1 id2">...</indexterm>

There is no way that this can fit into the semantics of an indexterm. Although it claims to be the start of a range, it does not have an xml:id for the end-of-range indexterm to point back to. In addition, it includes zoned terms, and mixing the two different methods for indicating a range in the same indexterm is probably a bad idea.

Common attributes and common linking attributes.

These elements contain indexterm: abbrev, accel, acknowledgements, acronym, address, annotation, answer, appendix, application, arg, article, artpagenums, attribution, authorinitials, bibliocoverage, bibliodiv, bibliography, biblioid, bibliolist, bibliomisc, bibliomixed, bibliomset, bibliorelation, bibliosource, blockquote, bridgehead, callout, calloutlist, caption (db.caption), caption (db.html.caption), caution, chapter, citation, citebiblioid, citetitle, city, classname, classsynopsisinfo, code, colophon, command, computeroutput, confdates, confnum, confsponsor, conftitle, constant, constraintdef, contractnum, contractsponsor, contrib, country, database, dedication, description, edition, email, emphasis (db._emphasis), emphasis (db.emphasis), entry, envar, errorcode, errorname, errortext, errortype, example, exceptionname, fax, figure, filename, firstname, firstterm (db._firstterm), firstterm (db.firstterm), footnote, foreignphrase (db._foreignphrase), foreignphrase (db.foreignphrase), formalpara, funcdef, funcparams, funcsynopsisinfo, function, givenname, glossary, glossdef, glossdiv, glossentry, glosslist, glosssee, glossseealso, glossterm (db._glossterm), glossterm (db.glossterm), guibutton, guiicon, guilabel, guimenu, guimenuitem, guisubmenu, hardware, holder, honorific, important, index, indexdiv, informalexample, informalfigure, informaltable (db.cals.informaltable), initializer, interfacename, issuenum, itemizedlist, jobtitle, keycap, keycode, keysym, label, legalnotice, lineage, lineannotation, link, listitem, literal, literallayout, manvolnum, markup, mathphrase, member, methodname, modifier, mousebutton, msgaud, msgexplan, msglevel, msgorig, msgtext, note, olink, option, optional, orderedlist, orgdiv, orgname, otheraddr, othername, package, pagenums, para, paramdef, parameter, partintro, personname, phone, phrase (db._phrase), phrase (db.phrase), pob, postcode, preface, primary, primaryie, procedure, productname, productnumber, programlisting, prompt, property, publishername, qandadiv, qandaset, question, quote (db._quote), quote (db.quote), refdescriptor, refentry, refentrytitle, refmeta, refmiscinfo, refname, refpurpose, refsect1, refsect2, refsect3, refsection, refsynopsisdiv, releaseinfo, remark, replaceable, result, returnvalue, revdescription, revnumber, revremark, screen, secondary, secondaryie, sect1, sect2, sect3, sect4, sect5, section, see, seealso, seealsoie, seeie, seg, segtitle, seriesvolnums, setindex, shortaffil, sidebar, simpara, simplesect, state, step, street, subscript, subtitle, superscript, surname, symbol, synopsis, systemitem, table (db.cals.table), tag, taskprerequisites, taskrelated, tasksummary, td, term, termdef, tertiary, tertiaryie, textobject, th, tip, title, titleabbrev, toc, tocdiv, tocentry, token, topic, trademark, type, uri, userinput, variablelist, varname, volumenum, warning, wordasword, year.

The following elements occur in indexterm: primary, secondary, see, seealso, tertiary.