For differently-abled people it is quite complicated to access content on the Internet. To improve this the W3C consortium issued a recommendation called WCAG - Web Content Accessibility Guidelines.
The <a href="http://www.w3.org/TR/WCAG10/">recommendation </a> defines 3 priority levels of the recommendations:
[Priority 1]
A Web content developer must satisfy this checkpoint. Otherwise, one or more groups will find it impossible to access information in the document. Satisfying this checkpoint is a basic requirement for some groups to be able to use Web documents.
[Priority 2]
A Web content developer should satisfy this checkpoint. Otherwise, one or more groups will find it difficult to access information in the document. Satisfying this checkpoint will remove significant barriers to accessing Web documents.
[Priority 3]
A Web content developer may address this checkpoint. Otherwise, one or more groups will find it somewhat difficult to access information in the document. Satisfying this checkpoint will improve access to Web documents.
However a lot of websites does not fulfill even the Priority 1 recommendations. We want to find a client-side solution for altering of such pages for the people with special needs.