docs: def next_unwrittable_on_row(view, coords):
      """Return position of the next (in row) letter that is unwrittable"""
      x, y = coords
      maxx = max(view.keys(), key=itemgetter(0))[0]
      for offset in range(x + 1, maxx):
          letter = view[offset, y]
          if letter not in REWRITABLE_LETTERS:
              return offset
      return None