Do you have to close all of your tags? Yes. Is the markup based on HTML with XML rules like closing tags? Yes. Do you even have to close the tags of your custom components? Yes. When generating your createElement sequence from JSX, does it create or close tags in a different order/hierarchy than what you specified in the JSX? No. Does it emit markup or element creation calls that match the parsing behavior of HTML5? No.

Walks like an XHTML duck. Talks like an XHTML duck. It's an XHTML duck despite the JS interop and the lack of DTD preamble.