From the introduction: "Speaking of general characteristics of tone languages, William S-Y-Wang (1967) points out some basic differences between the types of tone found in language areas of the world. Among other things, he notes that for some languages tone functions primarily to make lexical distinctions with the Sino Tibetan family being cited as examples of this type. For other languages tone functions primarily on the grammatical level. Otomanguean languages are cited as examples of this type. In light of this fact, it is not surprising that two types of tone perturbation need to be distinguished in Texmelucan Zapotec, hereafter referred to as TZ. The first type I will call Phonological Perturbation. This type consists of rules and processes operating in a phonological environment. The second type I will call Grammatical Perturbation. This type consists of phonological rules applying in grammatical environments and will be ordered along with the other syntactico-phonological rules. I will discuss the two types of perturbation in their respective order. I will then move on to a discussion of laryngealization and stress."
Speck, Charles H.
"Texmelucan Zapotec suprasegmental phonology,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 22, Article 9.
Available at: https://commons.und.edu/sil-work-papers/vol22/iss1/9