I think "foreign content" is still the weirdest state in HTML5. Outside of it, it's rather clear: Depending on the content type, you're either using the XML par

I think "foreign content" is still the weirdest state in HTML5. Outside of it, it's rather clear: Depending on the content type, you're either using the XML parser or the HTML5 parser which is just its own thing and entirely divorced from XML (and SGML). But during embedded SVG sections, you're still using the HTML5 parser, only that it temporarily pretends to read XML. I have no idea what the rules are there and what kind of subsets or supersets of XML the parser is accepting here.