If you’ve checked out the 12 Days of Web (HT to @mandaris for sharing), and you were curious as to why popover is an attribute rather than a HTML tag, this section from OpenUI’s post about the feature explains the reason.
a content attribute allows behavior to be applied to any element
while maintaining semantics of that element:
Semantics are provided by elements, and behaviors are confered on those elements via attributes. This situation is exactly analogous to
Yeah, okay. I can see why it was done that way.