tertiaryie — A tertiary term in an index entry, rather than in the text
tertiaryie ::=
abbrevaccelacronymaltanchorannotationapplicationauthorbibliorefcitationcitebiblioidciterefentrycitetitleclassnamecodecommandcomputeroutputconstantcorefdatabasedateeditoremailemphasis (db.emphasis)envarerrorcodeerrornameerrortexterrortypeexceptionnamefilenamefirsttermfootnotefootnoterefforeignphrasefunctionglosstermguibuttonguiiconguilabelguimenuguimenuitemguisubmenuhardwarehtml:buttonhtml:fieldsethtml:inputhtml:labelhtml:selecthtml:textareaindexterm (db.indexterm.endofrange)indexterm (db.indexterm.singular)indexterm (db.indexterm.startofrange)initializerinlineequationinlinemediaobjectinterfacenamekeycapkeycodekeycombokeysymlinkliteralmarkupmenuchoicemethodnamemodifiermousebuttonnonterminalolinkooclassooexceptionoointerfaceoptionoptionalorgnamepackageparameterpersonnamephrase (db.phrase)productnameproductnumberpromptpropertyquoteremarkreplaceablereturnvalueshortcutsubscriptsuperscriptsymbolsystemitemtagtermdeftokentrademarktypeuriuserinputvarnamewordaswordxrefTertiaryIE identifies a third-level word or
words in an IndexEntry.
In IndexEntrys, you can specify as many tertiary terms
that are necessary.  Secondary and tertiary terms can be mixed, following
the primary.
Formatted as a displayed block.
TertiaryIEs occur below the 
SecondaryIE, and are usually aligned with each other and indented
from the secondary.
Points to one or more internal link targets by identifying the value of their xml:id attributes
The following elements occur in tertiaryie: text, abbrev, accel, acronym, alt, anchor, annotation, application, author, biblioref, citation, citebiblioid, citerefentry, citetitle, classname, code, command, computeroutput, constant, coref, database, date, editor, email, emphasis (db.emphasis), envar, errorcode, errorname, errortext, errortype, exceptionname, filename, firstterm, footnote, footnoteref, foreignphrase, function, glossterm, guibutton, guiicon, guilabel, guimenu, guimenuitem, guisubmenu, hardware, html:button, html:fieldset, html:input, html:label, html:select, html:textarea, indexterm (db.indexterm.endofrange), indexterm (db.indexterm.singular), indexterm (db.indexterm.startofrange), initializer, inlineequation, inlinemediaobject, interfacename, keycap, keycode, keycombo, keysym, link, literal, markup, menuchoice, methodname, modifier, mousebutton, nonterminal, olink, ooclass, ooexception, oointerface, option, optional, orgname, package, parameter, personname, phrase (db.phrase), productname, productnumber, prompt, property, quote, remark, replaceable, returnvalue, shortcut, subscript, superscript, symbol, systemitem, tag, termdef, token, trademark, type, uri, userinput, varname, wordasword, xref.