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I took at look at Basecamp. They embed todo items in a UL, a little bit like XOXO (with a lot of extra schmutz). If you assign something to someone then you get something like this:
<span><strong>Smack Man:</strong> wonder why it looks like this</span>
so what's missing here is an identifier for the person, and their role. We'd imaging something like,
<span class="htodo"> <span class="attendee"><span class="hcard"><span class="nickname">Smack Man</span></span></span> <span class="summary">wonder why it looks like this</span> </span>
(the assignment looks a bit verbose.... plus "attendee" is not exactly the right idea, but it's coming from VTODO, we we defer.)