Comment 2 for bug 850520

@Keith

- a general solution, to get the content region of an app window (this is for Mac ;-)
- the app must be running in this case

ap = App("Preview")
top = 55
ap.focus()
win = ap.window()
content = win.above(1).below(top).below(win.h-top)
content.highlight(2)

so no need to capture/find the whole content.