Styling text with <span class='...'>?

"Jules" <[email protected]>
Newsgroups gmane.comp.mozilla.devel.editor
Message-ID <[email protected]> 
Does anyone know how I could apply a style to the current selection using a 
<span> element with a class attribute?  I'd be looking for some kind of 
script that works analogously to document.execCommand ("bold", false, ""), 
ideally with a query function that returns whether or not it is applied to 
the current selection.  Any ideas?  Has anyone implemented this?
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