Extra <p> around <div> in HTML output

[melisgl]

I'm trying to wrap a div around some Markdown and its HTML rendering with CSS, but the opening tag gets wrapped in a p, making it ineffective. Here is a small test case without any Markdown:

(with-output-to-string (out)
  (3bmd::print-doc-to-stream-using-format
   (3bmd-grammar:parse-doc (format nil "<div>~%~%</div>"))
   out :html))
=> "<p><div></p>
</div>
"

I'd expect the output to be <div></div> with two newlines in between them.
Similarly:

(with-output-to-string (out)
  (3bmd::print-doc-to-stream-using-format
   (3bmd-grammar:parse-doc (format nil "<div>~%~%- x~%- y~%~%</div>"))
   out :html))
=> "<p><div></p>

<ul>
<li>x</li>
<li>y</li>
</ul>
</div>
"

If I add a newlines after the closing tag, the Markdown inside is not processed:

(with-output-to-string (out)
  (3bmd::print-doc-to-stream-using-format
   (3bmd-grammar:parse-doc (format nil "<div>~%~%- x~%- y~%~%</div>~%"))
   out :html))
=> "<div>

- x
- y

</div>
"

For some reason, adding a space in front of the opening and closing tags unwraps the closing div:

(with-output-to-string (out)
  (3bmd::print-doc-to-stream-using-format
   (3bmd-grammar:parse-doc (format nil " <div>~%~%- x~%- y~%~% </div>~%"))
   out :html))
=> "<p><div></p>

<ul>
<li>x</li>
<li>y</li>
</ul>
 </div>
"

[melisgl]

Hmm, I've just realized that <p><div></p> ... <p></div></p> works.

See https://html.spec.whatwg.org/multipage/parsing.html#parsing-main-inbody:

A start tag whose tag name is one of: "address", "article", "aside", "blockquote", "center", "details", "dialog", "dir", "div", "dl", "fieldset", "figcaption", "figure", "footer", "header", "hgroup", "main", "menu", "nav", "ol", "p", "search", "section", "summary", "ul"
If the stack of open elements has a p element in button scope, then close a p element.

Insert an HTML element for the token.

So, <p><div></p> ... <p></div></p> is parsed as <p></p><div><p></p> ... <p></p></div><p></p>, which can lead to layout artifact, but this issue not terribly important.