code: def wait_for_element_by_selector(self, selector, seconds):
      
  
      def assert_element_present():
          """Assert an element matching the given selector exists."""
          if not find_elements_by_jquery(world.browser, selector):
              raise AssertionError("Expected a matching element.")
  
      wait_for(assert_element_present)(timeout=int(seconds))
docs: Assert an element exists matching the given selector within the given time
      period.