But STYLE isn't an HTML 2.0 element, so it would itself
be treated as unknown. (So would any other yet-to-be-invented
HEAD element with content.)
If the browser sees a (presumably legal HTML 2.1) document like:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML-NG Experimental//EN">
<HTML>
<HEAD>
<TITLE>Blah</TITLE>
<STYLE NOTATION=ARENA-STYLESHEET> <!-- unknown element in HEAD -->
...style specification...
</STYLE>
</HEAD>
<BODY>
...
</BODY>
</HTML>
the STYLE start-tag, since it's unknown by 2.0 browsers,
would by the above heuristic imply </HEAD><BODY>.
Then the current guidelines for dealing with unrecognized
elements would apply, and the "...style specification..."
would be rendered as plain text, which is undesired.
--joe@art.com