How to check current editor content

Hello,

I would like to access the editor content from javascript; there are many threads on this subject in the forum, but nobody seems to have a working answer...

Here's my problem: I want to check that a user has written something in the editor before submitting the form to the server.
For example, if the field was a regular textarea, I would do this checking that textarea.value.length>0. How can I accomplish this with FCKEditor?

I think that this is a FAQ (unanswered) that deserves to be included in the official documentation.

regards,
Alessandro