secondaryie — A secondary term in an index entry, rather than in the text
secondaryie ::=
abbrevaccelacronymaltanchorannotationapplicationauthorbibliorefcitationcitebiblioidciterefentrycitetitleclassnamecodecommandcomputeroutputconstantcorefdatabasedateeditoremailemphasis (db.emphasis)envarerrorcodeerrornameerrortexterrortypeexceptionnamefilenamefirsttermfootnotefootnoterefforeignphrasefunctionglosstermguibuttonguiiconguilabelguimenuguimenuitemguisubmenuhardwarehtml:buttonhtml:fieldsethtml:inputhtml:labelhtml:selecthtml:textareaindexterm (db.indexterm.endofrange)indexterm (db.indexterm.singular)indexterm (db.indexterm.startofrange)initializerinlineequationinlinemediaobjectinterfacenamekeycapkeycodekeycombokeysymlinkliteralmarkupmenuchoicemethodnamemodifiermousebuttonnonterminalolinkooclassooexceptionoointerfaceoptionoptionalorgnamepackageparameterpersonnamephrase (db.phrase)productnameproductnumberpromptpropertyquoteremarkreplaceablereturnvalueshortcutsubscriptsuperscriptsymbolsystemitemtagtermdeftokentrademarktypeuriuserinputvarnamewordaswordxrefSecondaryIE identifies a secondary word or
words in an IndexEntry.
In IndexEntrys, you can specify as many secondary terms
that are necessary.  Secondary and tertiary terms can be mixed, following
the primary.
Formatted as a displayed block.
SecondaryIEs occur below the 
PrimaryIE, usually aligned with each other and indented
from the primary.
Points to one or more internal link targets by identifying the value of their xml:id attributes
The following elements occur in secondaryie: 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.