Jacques Distler's "<abbr>, <acronym>, Accessibility & Automation" presents thoughts on the perennially discussed subject of marking up abbreviations. Many have argued that lack of Internet Explorer support for <abbr> is reason enough to markup all abbreviations (acronyms and initialisms) with <acronym>. Jacques disagrees: "...if these two elements are to be treated differently by aural browsers, then, on Accessibility grounds, you should be mindful of using the right one in each case."
In addition to using <abbr>, Jacques points out that it is necessary to markup all occurrences of abbreviations, not necessarily to provide definition, but to give cues to screenreaders. Jacques's technique for achieving this bears repeating here:
The best way to achieve these varied goals is, the first time you use the abbreviation, to give its definition,
<abbr title="Cold Dark Matter">CDM</abbr>, but on subsequent uses, to merely mark it up as<abbr>CDM</abbr>. This will satisfy the screenreaders, and can be hidden from visual browsers with code like
abbr, acronym {border:none;}
abbr[title], acronym[title] {border-bottom: 1px dotted black;}
Our practice in the past has been to provide any abbreviation's definition on only its first occurrence (in any context, like, say, a weblog entry) with <acronym>, a method, as Jacques mentions, that meets WCAG. Jacques has convinced us to embrace <abbr> and mark all abbreviations, not simply first occurrences.
Evan Goer has said about Jacques that he believes he "may well be the only person on the planet who understands the XHTML 1 specification and uses it properly." We're glad he's helping the rest of us get it right, too.