A number of additional characters are used with the International Phonetic Alphabet by linguists documenting the languages of China and neighboring countries, especially linguists based in China.
These letters are used by those who want symbols for five equally-spaced vowels in formant space.
These letters, sometimes mistakenly called "apical",[1][2] derive from Karlgren, from a turned ⟨ι⟩.
These letters are featural derivatives of ⟨ɕ⟩ and ⟨ʑ⟩.