> Browsers do not implement HTML+, HTML2, HTML3.2 HTML4, HTML4.01, etc, as separate versions. They all just have a single implementation that covers all these versions at once.
Yeah, sure. Pay no attention to all these "if (is_html4.2)" statements inside the source code.
Browsers indeed usually have a single implementation of layout engine, because even a single implementation is overwhelmingly complex. Having several implementations would be impossible to maintain.
And they're getting even more complex. We now have CSS-based tables, flexible layouts and so on. Except that they all work like shit.