There are existing software systems that are HTML based. For instance, the MovableType that I (along with many others) use for blogging is written in Perl and generates HTML forms for its admin interface. The admin forms have a lot of functionality and I think MovableType is fairly good overall. But there are controls on some forms that I wish were a lot richer in functionality.

For instance, I'm typing this post into an HTML TEXTAREA control. If I right click on the control there is no Search option to search for a piece of text in the control. So if I saw a typo in the posted version of this while looking at my blog main page I'd still have to visually scan for it in the editing form. Well, it would be nice to able to override the TEXTAREA control and tell Mozilla (which is the browser I'm using) to use some other functionally richer control for any control on any page that calls out TEXTAREA. Then I'd be able to use a control that had a spell checker, a search facility, and even some macro defineable keys to make it easier to insert common text strings into my posts (eg the skeleton of an A HREF open and close tag pair). One could even add a TEXTAREA control that was a full HTML editor.

One advantage of being able to tell the browser to use some richer version of TEXTAREA is that one doesn't have to have access to the source code of the server app that generates the pages in order to enhance the functionality of the pages.

Of course browsers would need a plug-in facility that allowed users to add replacement versions of common controls. One way to do that which would be portable would be to allow replacement HTML controls to be coded in Java.