[niconii]

You have to know about what breaks out of <p> tags regardless of whether or not you leave off the end tag, though.

<p><div></div></p> is invalid HTML because <div> ends the paragraph, resulting in an unpaired </p>.

[anjbe]

And not just because of that. In XHTML‐as‐XML, where <div> does not implicitly end the paragraph, what you posted is still invalid because <p> cannot contain <div>.