docs: def _sprite_file(map, sprite):
      """
      Returns the relative path (from the images directory) to the original file
      used when construction the sprite. This is suitable for passing to the
      image_width and image_height helpers.
      """
      map = StringValue(map).value
      sprite_name = StringValue(sprite).value
      sprite_map = sprite_maps.get(map)
      sprite = sprite_map and sprite_map.get(sprite_name)
      if not sprite_map:
          log.error("No sprite map found: %s", map)
      elif not sprite:
          log.error("No sprite found: %s in %s", sprite_name, sprite_map['*n*'])
      if sprite:
          return QuotedStringValue(sprite[1][0])
      return StringValue(None)