docs: def next_line(self, require_prefix=True):
          """Return the next line in the source.
  
          :param require_prefix:  if False, the whole line will be returned.
              otherwise, return the line with prefix stripped or None if the prefix
              is not matched.
          """
          if require_prefix:
              m = self.expect_re(r'(?m)[^\n]*?$\n?')
          else:
              m = self._expect_re(r'(?m)[^\n]*$\n?', self.pos)
          self.match = m
          if m:
              return m.group()