message: Add a note to Util::IsAcceptableCharacterAsCandidate.
diff: @@ -1443,6 +1443,9 @@ bool Util::IsAcceptableCharacterAsCandidate(char32 letter) {
  // Bidirectional text control are not acceptable.
  // See: https://en.wikipedia.org/wiki/Bidirectional_text
  + // Note: Bidirectional text controls can be allowed, as it can be contained in
  + // some emoticons. If they are found not to be harmful for the system, this
  + // section of validation can be abolished.
  if (letter == 0x061C || letter == 0x200E || letter == 0x200F ||
  (0x202A <= letter && letter <= 0x202E) ||
  (0x2066 <= letter && letter <= 0x2069)) {
  