Modifier Tone Letters is a Unicode block containing tone markings for Chinese, Chinantec, Africanist, and other phonetic transcriptions. It does not contain the standard IPA tone marks, which are found in Spacing Modifier Letters.
⟨꜀◌ ꜁◌ ꜂◌ ꜃◌ ◌꜄ ◌꜅ ◌꜆ ◌꜇⟩ are used to mark yin and (underlined) yang splits of the ping, shang, qu and ru tones, respectively, in the etymological four-tone analysis of Chinese. The dotted tone letters ⟨꜈ ꜉ ꜊ ꜋ ꜌⟩ are used for the pitch of neutral tones, while the reversed tone letters ⟨꜒ ꜓ ꜔ ꜕ ꜖⟩ and neutral ⟨꜍ ꜎ ꜏ ꜐ ꜑⟩ are used for tone sandhi. ⟨ ꜗ ꜘ ꜙ ꜚ ⟩ are modifier letters used in Ozumacín Chinantec. ⟨ꜛ ꜜ⟩ are the IPA modifier letters for upstep and downstep, while ⟨ꜝ ꜞ ꜟ⟩ are substitutes people used before broad font support of the IPA, and still preferred by some.
The following Unicode-related documents record the purpose and process of defining specific characters in the Modifier Tone Letters block: