docs: def _source_info():
      """
      Get information from the user's code (two frames up)
      to leave breadcrumbs for file, line, class and function.
      """
      ofi = inspect.getouterframes(inspect.currentframe())[2]
      try:
          calling_class = ofi[0].f_locals['self'].__class__
      except KeyError:
          calling_class = None
      # Tuple of file,line,calling_class,function_name
      return ofi[1], ofi[2], calling_class, ofi[3]