[idn] stringprep comment 5: hangul conjoining sequence

["Soobok Lee" <lsb@postel.co.kr>]

Two issues briefed in hangulchars drafts and in this mailling list, but not mentions in
  the latest nameprep and stringprep drafts:

 1. When  old trailing hangul jamos are included in conjoining jamo sequences, UAX15(NFC)
     performs  partial combinations to produce  "a modern hangul syllable(LV) + a standalone
      old hangul jamo(oT)" and that form satify a ridiculous syllable break condition (X.T) .


 2. UAX15 also tries ridiculous partial combinations when it met a combining sequence if
      two or more leading hangul jamos followed by hangul vowel jamos, and produce
      a syllable break condition (L.LV)

 3. Compatibility hangul jamos are mapped into conjoining jamos without any fillers.

 Errors briefed in 1,2 and 3 came from  past poor cooperations between UAX15 authors and Korean UTC participants, and NFC routines
was already widely distributed.

 Now I propose UTC make new normalizations (call it NFN)to correct such errors and faults and
    let stringprep include it after casefolding : that is  NFKC(NFN(casefold(x)).

 We dont need to modify NFC and NFKC. Just add new correcting normalizations as soon as possible.

 Stringprep efforts should be in sync with further UTC's works. No hastes!

 Soobok Lee