[mixedCase]

We're talking XML rather than HTML (and omitting certain closing tags isn't compliant HTML5 anyway).

In XML there's also the concept of using self-closing tags only for "empty tags". Meaning, <tagname val="123"/> isn't "correct" and <tagname>123</tagname> should be used instead; while s-expressions simplify this.

[tannhaeuser]

Sorry but your comment re XML is incorrect. I suggest you study the HTML and XML specs, especially if want to convince us of an alternate XML serialization.