Lets just get something straight. I didn't mean doing HTML5 validation in Expression tools. I meant having a palette and brushes and doing vector art on a stage visually and tweening where it's pre-rendered for debugging and finally compiled to HTML5 canvas drawing and javascript automatically.

From the job details it's really unclear what aspect of HTML5 they are building into the Expression tools.

HTML5 constructs can be as mundane as semantic header, nav and footer tags or can be as spectacular as what flash does via animation using canvas and javascript worker threads, and local storage.

So while it's promising that they're looking for employees with some HTML5 knowledge, it's not promising that they're not talking about making this tool. Before you do something at a company that size there has to be some outward discussion.