how can I use a string which can be edited by the HTMLArea widget in an XML binding?
I'm afraid you'll have to do parsing/serialization by hand in your code. An HTMLArea is just a textarea with some DHTML and there is no support in CForms, AFAIK, for binding an XML document to a widget. It would be a welcome addition, though.
HTMLArea should only produce well-formed XHTML, though, so there is no need to filter it with JTidy or such before parsing.
Ugo
