code: func uniCharCode(a, b, c, d rune) rune {
  	return rune(char2hex(a)<<12 | char2hex(b)<<8 | char2hex(c)<<4 | char2hex(d))
  }
docs: // Converts four hexadecimal chars to the integer that the
  // string represents. For example, uniCharCode('0','0','0','f')
  // will return 15, and uniCharCode('0','0','f','f') returns 255.
  // Returns a negative number on error, if a char was invalid.
  // This is implemented by noting that char2hex() returns -1 on error,
  // which means the result of ORing the char2hex() will also be negative.