[gsnedders]

No, we decided that what was important was interoperable implementations: it doesn't matter how you achieve that goal. What's needed is specs that define how to handle all input (it doesn't matter what the spec says: it can define how to handle every single last possible case as HTML5 does, or it can define a subset of inputs to trigger some fatal error handling as XML1.0 does) and sufficient test suites that implementers catch bugs in their code before it ships (and the web potentially starts relying on their quirks).

The problem with IE6 was the fact that it wasn't interoperable (in many cases, every implementation was conforming according to the spec, and there were frequently differences in behaviour in valid input that the spec didn't fully define) and the fact that it had lots of proprietary extensions (and being strict and disallowing any extensions makes it hard to extend formats in general in a non-proprietary way; one option is strict versioning but then you end up with a million if statements all over the implementation to alter behaviour depending on the version of the content).

Some of the worst issues with IE that took the longest for other browsers to match were things like table layout: IE quite closely matched NN4 having invested a lot in reverse-engineering that as the web depended on the NN4 behaviour in places; Gecko had rewritten all the table layout code from NN and didn't match its behaviour having been written according to the specs which scarcely define how to layout any table even today.