docs: def is_zh(ch):
      """return True if ch is Chinese character.
      full-width puncts/latins are not counted in.
      """
      x = ord(ch)
      # CJK Radicals Supplement and Kangxi radicals
      if 0x2e80 <= x <= 0x2fef:
          return True
      # CJK Unified Ideographs Extension A
      elif 0x3400 <= x <= 0x4dbf:
          return True
      # CJK Unified Ideographs
      elif 0x4e00 <= x <= 0x9fbb:
          return True
      # CJK Compatibility Ideographs
      elif 0xf900 <= x <= 0xfad9:
          return True
      # CJK Unified Ideographs Extension B
      elif 0x20000 <= x <= 0x2a6df:
          return True
      else:
          return False