U+02E5 ˥ MODIFIER LETTER EXTRA-HIGH TONE BAR ,HTML:˥ U+02E6 ˦ MODIFIER LETTER HIGH TONE BAR ,HTML:˦ U+02E7 ˧ MODIFIER LETTER MID TONE BAR ,HTML:˧
characters from a normal ASCII keyboard. "HK" stands for two other case-sensitive letter-to-letter transliteration schemes: Harvard-Kyoto and XIAST scheme. Both