Tone letters are written characters that represent the tones of a language, especially contour tones, that were invented by Yuen Ren Chao and adopted into the International Phonetic Alphabet.
Tone letters are written characters. These characters represent the tones of a language, especially contour tones. Contour tones were invented by Yuen Ren Chao. Contour tones were adopted into the International Phonetic Alphabet.