docs: def _filldown(self, lineno):
          """
          Copy current_context into `lines` down up until lineno
          """
          if self.line > lineno:
              # XXX decorated functions make us jump backwards.
              # understand this more
              return
  
          self.lines.extend(
              self.current_context for _ in range(self.line, lineno))
          self.line = lineno