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.

any attribute

Any attribute in any other explicit namespace

class

Identifies the class of index term

Enumerated values:
“startofrange”	The start of a range

pagenum

Indicates the page on which this index term occurs in some version of the printed document

scope

Specifies the scope of the index term

Enumerated values:
“all”	All indexes
“global”	The global index (as for a combined index of a set of books)
“local”	The local index (the index for this document only)

significance

Specifies the significance of the term

Enumerated values:
“normal”	Normal
“preferred”	Preferred

type

Specifies the target index for this term

zone

Specifies the IDs of the elements to which this term applies

These elements contain indexterm: abbrev, abstract, 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, buildtarget, 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, danger, database, dedication, description, edition, email, emphasis (db._emphasis), emphasis (db.emphasis), entry, enumidentifier, enumitemdescription, enumname, enumvalue, 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, macroname, manvolnum, markup, mathphrase, member, meta (db.meta.content), 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, specializedtemplate, state, step, street, subscript, subtitle, superscript, surname, symbol, synopsis, synopsisinfo, systemitem, table (db.cals.table), tag, taskprerequisites, taskrelated, tasksummary, td, template, templatename, term, termdef, tertiary, tertiaryie, textobject, th, tip, title, titleabbrev, toc, tocdiv, tocentry, token, topic, trademark, type, typedefname, unionname, uri, userinput, variablelist, varname, volumenum, warning, wordasword, year.

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