Hey, just so that maybe others avoid falling into the same trap:
I felt at first that it would be nicer to use marks for certain kinds of things both on block and inline nodes. Mainly this was for reasons of consistency. And with some additions here and there to make surre to use
<div> for marks on block nodes and
<span> for inline nodes, it did actually work for most basic node types.
Problems started when I needed to add marks to list items. Because marks always need to wrap around the element they are marking, that would basically create HTML such as this:
<ul> <div class="mark"> <li></li> </div> </ul>
And that’s just not valid HTML. I guess trying to tag table cells or rows would have given me similar problems.