This is a heads-up that we will shortly start landing patches for
a new WebKit framework that we at Apple have been working on for a
while. We currently call this new framework ‘WebKit2’.

WebKit2 is designed from the ground up to support a split process
model, where the web content (JavaScript, HTML, layout, etc) lives
in a separate process. This model is similar to what Google Chrome
offers, with the major difference being that we have built the
process split model directly into the framework, allowing other
clients to use it.

As Gruber says at Daring Fireball….

Whoa.

What does this mean? If a tab or another window locks up, you can terminate (in theory) just that one tab or Window. If a Window or tab locks up, it shouldn’t lock up the entire browser, your other windows should still continue to work.

Chrome has these features, but Webkit is used by a variety of other browsers, even on other platforms, so this is big.