The Evolution of Web Platform Tests

The old engine is more featureful and it supports a much wider swath of the web. But the new engine is huge, much more closely to the classification and should have support for properly fragmenting content. Fragmentation is this process of taking different parts of the layout tree and spreading them. And then also we have made this change with regard to parallelization. When you're laying out the web, in general, things can be done in parallel. But there are moments where you have to do things in serial such as floats or CSS content. So that's something that would have been very difficult with the old layout tree.