They can't produce imbalanced tags because it's impossible to represent in a DOM tree.
They will indeed auto close the (first) paragraph, and also auto open a new <p> element because of the extra closing </p> tag.
Try it out by typing this in your address bar and open the inspector:
data:text/html;charset=utf-8,<!DOCTYPE html><p><div>hello</div></p>
The generated HTML (document.body.parentNode.innerHTML):
<head></head><body><p></p><div>hello</div><p></p></body>
Browsers will go out of their way to produce a (valid) DOM from pretty much any string (as per the HTML5 spec). (Almost?) nothing is a syntax error. You won't get a HTML5-compliant browser to show a parse error to the user in HTML (of course, this is not the case in XHTML).
edit: sorry niconii, I edited my comment under your feet.
They will indeed auto close the (first) paragraph, and also auto open a new <p> element because of the extra closing </p> tag.
Try it out by typing this in your address bar and open the inspector:
The generated HTML (document.body.parentNode.innerHTML): Browsers will go out of their way to produce a (valid) DOM from pretty much any string (as per the HTML5 spec). (Almost?) nothing is a syntax error. You won't get a HTML5-compliant browser to show a parse error to the user in HTML (of course, this is not the case in XHTML).edit: sorry niconii, I edited my comment under your feet.