Formatted inline.

Optional arguments in a synopsis are usually given special typographic treatment, and often they are surrounded by square brackets. The optional tag is expected to generate the brackets.

Outside a synopsis, the typographic treatment of optional is application specific.

Common linking attributes.

any attribute

Any attribute in any other explicit namespace

These elements contain optional: bridgehead, caption (db.html.caption), citation, citetitle, classsynopsisinfo, computeroutput, contrib, emphasis (db.emphasis), entry, enumitemdescription, firstterm (db.firstterm), funcsynopsisinfo, glosssee, glossseealso, glossterm (db.glossterm), link, literallayout, member, meta (db.meta.content), olink, optional, orgdiv, para, phrase (db.phrase), primary, primaryie, programlisting, quote (db.quote), refdescriptor, refentrytitle, refname, refpurpose, remark, screen, secondary, secondaryie, see, seealso, seealsoie, seeie, seg, segtitle, simpara, subtitle, synopsis, synopsisinfo, td, term, termdef, tertiary, tertiaryie, th, title, titleabbrev, tocentry, userinput.

The following elements occur in optional: text, abbrev, acronym, alt, anchor, annotation, biblioref, coref, date, emphasis (db._emphasis), firstterm (db._firstterm), footnote, footnoteref, foreignphrase (db._foreignphrase), glossterm (db._glossterm), indexterm (db.indexterm.endofrange), indexterm (db.indexterm.singular), indexterm (db.indexterm.startofrange), inlinemediaobject, link, olink, optional, phrase (db._phrase), quote (db._quote), remark, replaceable, subscript, superscript, trademark, wordasword, xref.