code: def extract_selector_info(sel):
      
      #  walk the parsed_tree, looking for pseudoClass selectors, check names
      # add in steps and/or deferred extras
      steps, extras = _extract_sel_info(sel.parsed_tree)
      steps = sorted(set(steps))
      extras = sorted(set(extras))
      if len(steps) == 0:
          steps = ['default']
      return (steps, extras)
docs: Return selector special pseudo class info (steps and other).