feat: support self closing tags such as <p/>

[berenddeboer]

Currently they lead to parser errors, but this is perfectly valid HTML.

[hecrj]

Hey, thanks!

I took a quick look when you opened the PR but I forgot to comment. Sorry!

Is this documented somewhere in the HTML 5 spec? I believe it mentions a self-closing slash is only allowed in void elements and foreign elements.

We already handle an optional slash in void elements here:

html-parser/src/Html/Parser.elm

Lines 208 to 214 in 6ffc165

	if isVoidElement name then
	Parser.succeed (Element name attributes [])
	|. Parser.oneOf
	[ Parser.chompIf ((==) '/')
	, Parser.succeed ()
	]
	|. Parser.chompIf ((==) '>')

[berenddeboer]

Regardless whether it is allowed, it's pretty common! All browsers handle it. I would say html-parser probably should not try to be a validating parser, that's an entirely different thing. And besides the parser currently accepts many forms of HTML that are technically not valid.

is not a void element, so adding it to the void element list does not work. It can have many other tags.

[berenddeboer]

Secondly if the output comes via XML (XHTML 5.0), this could easily be generated. I.e. it's perfectly valid xml.