> Counter argument: then why do conditional comments behave differently in each browser engine?
They don't. IE5-9 sees conditional comments specially, others don't.
> I am not talking about trident, but about CSS hacks for presto, gecko, webkit and blink as well.
CSS isn't HTML5, and those hacks aren't conditional comments, and don't rely on parsing differences.
> If every browser would render as specified
The claim was about parsing HTML5 and generating a DOM, not rendering.
> Counter argument: then why do conditional comments behave differently in each browser engine?
They don't. IE5-9 sees conditional comments specially, others don't.
> I am not talking about trident, but about CSS hacks for presto, gecko, webkit and blink as well.
CSS isn't HTML5, and those hacks aren't conditional comments, and don't rely on parsing differences.
> If every browser would render as specified
The claim was about parsing HTML5 and generating a DOM, not rendering.