message was raised if the renderer name was not a string.

  to encode a Unicode ``path`` into ASCII before attempting to split
  it and decode its segments.  This is for convenience, effectively to
  allow a (stored-as-Unicode-in-a-database, or
  retrieved-as-Unicode-from-a-request-parameter) Unicode path to be
  passed to ``find_model``, which eventually internally uses the
  ``traversal_path`` function under the hood.  In version 1.2 and
  prior, if the ``path`` was Unicode, that Unicode was split on
  slashes and each resulting segment value was Unicode.  An
  inappropriate call to the ``decode()`` method of a resulting Unicode
  path segment could cause a ``UnicodeDecodeError`` to occur even if
  the Unicode representation of the path contained no 'high order'
  characters (it effectively did a "double decode").  By converting
  the Unicode path argument to ASCII before we attempt to decode and
  split, genuine errors will occur in a more obvious place while also
  allowing us to handle (for convenience) the case that it's a Unicode
  representation formed entirely from ASCII-compatible characters.