In Mexican linguistics, saltillo is the word for a glottal stop consonant. The name was given by the early grammarians of Classical Nahuatl. In a number of other Nahuan languages, the sound cognate to the glottal stop of Classical Nahuatl is, and the term saltillo is applied to either pronunciation. The saltillo is often written with an apostrophe, though it is sometimes written for either pronunciation, or when pronounced. The spelling of the glottal stop with an apostrophe-like character most likely originates from transliterations of the Arabic hamza. It has also been written with a grave accent over the preceding vowel in some Nahuatl works, following Horacio Carochi. The saltillo represents a phoneme in many other indigenous languages of the Americas and so its presence or absence can distinguish words. However, there is no saltillo in Standard Spanish, so the sound is often imperceptible to Spanish speakers, and Spanish writers usually did not write it when transcribing Mexican languages: Nahuatl "in a fire" and "he ascends" were both typically written tleco, for example. Where saltillo is distinguished, the latter may be written tlehko or tleꞌko.
The saltillo letter
Although the basic meaning of the word 'saltillo' is the sound, it is often applied to the letter used to write that sound, especially the straight apostrophe. The alphabet of the Tlapanec language uses both uppercase and lowercase saltillos,. Unicode support of the cased forms began with Unicode 5.1, with and. Both are typically rendered with a straight apostrophe-like shape sometimes described as a dotless exclamation point. Typesetters who are unfamiliar with Unicode frequently use an apostrophe instead, but that can cause problems in electronic files because the apostrophe is a punctuation mark, not a word-building character, and the ambiguous use of apostrophe for two different functions can make automated processing of the text difficult. The lowercase saltillo letter is used in Miꞌkmaq of Canada, Izere of Nigeria and in at least one Southeast Asian language, Central Sinama of the Philippines and Malaysia. In the latter it represents both the glottal stop and the centralized vowel and derives from the historical use of hamza for those sounds inArabic script. Examples are bowaꞌ 'mouth' as a consonant and nsꞌllan 'oil' as a vowel.