Version 1 of Generating Accessible HTML

I'm interested in writing a Tcl package to aid in the generation of web-based HTML, especially forms, that is accessible to users with disabilities. I'm already well-versed in writing accessible HTML, but I'm unsure where to begin on the Tcl side of things:

I'd like this package to work well with the existing HTML package, what are some things to keep in mind when subclassing (if that's the proper term) a package in Tcl?