Showing important keywords in page margin

Hi!


I would like to generate a HTML Help, where the HTML files would look 
like this:

A big empty margin on the right side (about 200px). For some paragraphs 
there is a keyword or a phrase in that empty margin. So when user 
scrolls the page (the pages are supposed to be a few screens long), they 
can quickly look into that empty margin, find the keyword, and then read 
the related paragraph.

I hope I described it clearly. Many paper textbooks use this.


Please help me with this. First, which DocBook element should I use for 
those keywords / phrases? Second, do the default DocBook XSL stylesheets 
support this somehow; or would it be easy to add; or would it be 
difficult? (I have some knowledge of XSL language.) What would be the 
best way to do it?


Viliam Bur