As a Commons user, I am unsure what Assign Tags means

Two usability study content creators didn’t understand what to do with Assigned Tags section on node edit forms. They clicked on assigned tags + icon, the label and inside the field itself several times, hoping for some more instructions or information.

Create Blog entry | Commons Demo 5
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One possible solution is to collapse the fieldset. If they need it, they'll open it. If they don't, hopefully it won't cause them to stop and think.