Javascript validation with PHP-invoked editor

Hi,

I've been looking for an example of how to validate one of many fCKEditor instances on one of my pages.

Here is a trimmed down code snippet:

            $returnaction             = 'variable';
            $oFCKeditor             = new FCKeditor('abc');
            $oFCKeditor->BasePath       = '/fckeditor/';
            $oFCKeditor->Value          = $abc;
            $editor_abc            = $oFCKeditor->Create();

            $returnaction             = 'variable';
            $oFCKeditor             = new FCKeditor('def');
            $oFCKeditor->BasePath       = '/fckeditor/';
            $oFCKeditor->Value          = $def;
            $editor_def            = $oFCKeditor->Create();

So the page has two text boxes, editor_abc and editor_def. I need to require editor_def be filled out prior to submission, on the client side (javascript).

I've gone through all 5 php example files, but didn't see a validation example.

How is this accomplished?