> Another solution I've been considering is the possibility of using the
> same CSS to float a symbol or image to the left/right whenever there is
> a marginal gloss and have the content of this gloss appear in the ALT or
> xhtml title attributes and hence pop-up as a tooltip on hovering. The
> immediate problem with this is that such tooltips don't allow the parsed
> rendering of their content -a s far as I am aware.
No, but you don't need to use the browser's native "tooltip" implementation
(which in any case leads to various portability problems). Float your symbol
into the margin, and make it trigger a mouse-over event whose handler reads
the id of the trigger and uses it to look-up the expanded text, which you
can then write into a popup window (or a dedicated <div> on your display)
using whatever rendering tags you like.