Where is the expression window in Xcode 4?

Question

How can I add an expression to watch in Xcode 4?

This should be very obvious, but it is not. It does not seem to be down any menu or available on a contextual click

Answer 1

Just a note: I had a problem with expressions that they didn't get evaluated (Expression in Xcode 4.3.2 Debug area not evaluated).

To make it working, I had to include also the result type of the expression (e.g. (NSString *)[tag name]).