code: def parse_selectors(self, raw_selectors):
          
          # Fix tabs and spaces in selectors
          raw_selectors = _spaces_re.sub(' ', raw_selectors)
  
          parts = _xcss_extends_re.split(raw_selectors, 1)  # handle old xCSS extends
          if len(parts) > 1:
              unparsed_selectors, unsplit_parents = parts
              # Multiple `extends` are delimited by `&`
              unparsed_parents = unsplit_parents.split('&')
          else:
              unparsed_selectors, = parts
              unparsed_parents = ()
  
          selectors = Selector.parse_many(unparsed_selectors)
          parents = [Selector.parse_one(parent) for parent in unparsed_parents]
  
          return selectors, parents
docs: Parses out the old xCSS "foo extends bar" syntax.
  
          Returns a 2-tuple: a set of selectors, and a set of extended selectors.