code: func (c *Charmap) NewDecoder() *encoding.Decoder {
  	c.Init()
  	return &encoding.Decoder{Transformer: &cmapDecoder{runes: c.runes}}
  }
docs: // NewDecoder returns a Decoder the converts from the 8-bit
  // character set to UTF-8.  Unknown mappings, if any, are mapped
  // to '\uFFFD'.