You can build apps in HTML using Adobe AIR which parses it using Webkit, can this be done in Flash?
For example you have a string that contains <html><body><b>hello world</b></body></html> and then call a function that runs the WebKit parser over it and then outputs 'hello world' in bold to the stage?
Nope...that works just in AIR.
Closest thing you've got is this HTMLWrapper library as far as I know. Not the same thing, but could be handy.
Using the htmlText property of a multiline TextField object could be a substitute, although very limited. (You can use text formatting tags like <b>, lists, <p>, <span>, <img> and I guess that's about it.)