You use attach_browser() to test content on another browser instance,
see the example below:
click_link("Show popup window")
popup_win = attach_browser(:title, "For Testing iTest2 Popups")
# using Watir syntax
popup_win.link(:text, "Ok").click
popup_win.close
# continue on the parent page
click_link("iTest2")
In RWebSpec, the operations not on original browser window must use
Watir Syntax.
Check out the popup_window_spec.rb under samples project.
Cheers,
Zhimin