docs: def extract_syntax(self, syntax):
          """Parse and extract color/markup syntax from a format string."""
          tokens = syntax.split(self._COLOR_DELIM)
          r = [None, None]
  
          for token in tokens:
              for i, e in enumerate(('fg=', 'bg=')):
                  if token.startswith(e):
                      r[i] = token[3:]
  
              if r == [None, None]:
                  raise ColorSyntaxError("Unexpected color syntax '{0}'"
                                         .format(token))
  
          return tuple(r)