Textarea with formatting information

Hello,

I would like to ask you all for help once more.
Anytime it comes to a discussion about using XForms-based user interfaces in a project for structured content acquisition, our customers ask for the possibility to insert formatted text into a textarea. This user requirement is often a very critical one.
I am sure that some of you are already familiar with such kind of requirements and I would therefore like to ask you for useful input, how I can solve that. 

wbr,
Roman