about , the realization of which varies considerably from place to place and even within a single dialect How to write the saltillo. The "saltillo" is the name given by early grammarians to the phoneme that is phonetically a glottal stop () (particularly in classical Nahuatl) or an (in most contemporary dialects). This phoneme was usually not represented in the colonial period, except by Horacio Carochi who represented it with an acute accent over the preceding vowel. Today, in the dialects that pronounce the saltillo as it is frequently written with j, h. Some neo-classical orthographies use the letter h to represent the glottal stop of classical Nahuatl. Whether and how to represent vowel length Whether and how to represent allophones (sound variants), which approximate different Spanish phonemes, especially variants of o which come close to u To what extent writing in one variant should be adapted towards what is used in other variants. Historical transcription methodologies When the Spanish friars began transcribing Nahuatl into the Latin alphabet they, naturally, made use of Spanish language practices as a basis for the Nahuatl script. While the voiceless postalveolar affricate (English sound as in "church"), the voiceless postalveolar fricative (English sound as in "sure" and "cash"), and the voiceless stops () sounded the same in both Spanish and Nahuatl, Spanish lacked the voiceless alveolar affricate , the lateral alveolar affricate , and the glottal stop (the break between the vowels in English Uh-oh). Thus, Nahuatl written in the Latin alphabet is very similar to that of Spanish with a few exceptions: Words are stressed on the second-to-the-last vowel (excluding ) does not occur as an independent vowel. represents (as it did in Spanish; the Spanish phoneme transcribed with later shifted to a voiceless velar fricative, now written in most cases, while the Náhuatl phoneme transcribed with remained unchanged). represents a geminated . is , a voiceless alveolar lateral affricate. This is a phoneme not found in any European languages but commonly found in indigenous North and Central American languages (similar sounds exist in Welsh and Icelandic). and both represent . and both represent . without an adjacent represents a glottal stop. represents (as in Latin American Spanish or Basque). In post-colonial times Nahuatl had no standardized orthography, and colonial documents employ widely different orthographies: and both represent . alone may replace or to represent . The glottal stop may or may not