[pas]

it can be, but because it started as an SGML language (and nowadays who knows what it is) it allows ambiguous structures, plus it doesn't support arbitrary tags, whereas in XML the structure is strict but the tag schema is completely free.

[bazoom42]

Html does not allow ambigous structures. While it has a more flexible syntax than XML, it always parse to an unambigous structure.

[pas]

sure, but many browsers support quirks to render malformed HTML, right?