[shakna]

XHTML came after HTML 4.0, so it had its advent around the rise of JavaScript's popularity.

However, HTML 2.0, which you can find specified here [0], and it specifies the "ignore" behaviour. Short of spinning up an old VM, I think I'll trust that my memory hasn't failed me.

From RFC 1866:

> markup in the form of a start-tag or end-tag, whose generic identifier is not declared is mapped to nothing during tokenization. Undeclared attributes are treated similarly...

> For example: > <div class=chapter><h1>foo</h1><p>...</div> > => <H1>,"foo",</H1>,<P>,"..."

[0] https://www.w3.org/MarkUp/html-spec/

[bawolff]

If that was true, why did <script> tags have that horrible hack where the contents started with <!-- to hide from old browsers?

[shakna]

Note that in the example code I gave the enclosing tag vanished, but the internal tags did not. That's why.