docs: def scan(src):
          """ Scan scss from string and return nodes.
          """
          assert isinstance(src, (unicode_, bytes_))
          try:
              nodes = STYLESHEET.parseString(src, parseAll=True)
              return nodes
          except ParseBaseException:
              err = sys.exc_info()[1]
              print(err.line, file=sys.stderr)
              print(" " * (err.column - 1) + "^", file=sys.stderr)
              print(err, file=sys.stderr)
              sys.exit(1)