The world of generalized content markup (such as HTML) is complimented by markup specifications that provide more precise and explicit markup for particular knowledge domains (such as MathML in the domain of mathematics). Users who rely on assistive technologies (AT) also require domain sensitive rendering of specialized markup in order to use such content effectively. In fact domain specific content is often not usable if the user can rely only on generalized, off the shelf renderin from AT. The Open A11y Expert Handlers Workgroup is exploring opportunities for specifying a standardized plugin mechanism that would allow both open source and proprietary assistive rendering technology to take-over rendering from general, host AT while the user is focused on particular domain specific markup.