One criteria for accessible sites is, that abbrevations or acronyms are marked with the <abbr title=.. lang=..> markup.

Markup Proposal taken from http://moinmo.in/ParserMarket/Abbreviation:

* ^WAI^  Marks the word WAI as an abbreviation and tries to retrieve the explanation from the standard abbreviation definitions page "AbbrDict" 

* ^WAI|OtherPage^ Marks the word WAI as an abbreviation and tries to retrieve the explanation from the specified page "OtherPage".       

* ^WAI:Web Accessibility Initiative^ Marks the word WAI as an abbreviation and uses the given explanation.

* ^WAI|language=de^, ^WAI|OtherPage|language=de^, ^WAI:Web Accessibility Initiative|language=de^  Marks the word WAI as an foreign language abbreviation (compared to the language default of the wiki and the page)

Since the <acronym> tag won't be probably part of future (X)HTML standards, only <abbr> is used in Moin to mark acronyms and abbreviations.