def on(page_class, browser = @browser)
      page = page_class.new(browser)
      yield page if block_given?
      page
    end
def on(page_class, browser = @browser)
      page = page_class.new(browser)
      yield page if block_given?
      page
    end
Initializes and returns an instance of the given page class. Yields the
 page instance to a block if given.

 @param page_class [Class] the page class
 @param browser [Object] the browser instance
 @yield [page] yields page instance to a block