The Thai alphabet is derived from the Khmer alphabet (อักขระเขมร), which is modeled after the Brahmic script from the Indic family. Much like the Burmese adopted the Mon script (which also has Indic origins), the Thais adopted and modified Khmer script to create their own writing system. While the oldest known inscription in the Khmer language dates from 611 AD, inscriptions in Thai writing began to appear around 1292 AD. Notable features include:
1. It is an abugida script, in which the implicit vowel is a short /a/ for consonants standing alone and a short /o/ if the initial consonant or cluster is followed by another consonant.
2. Tone markers are placed above the initial consonant of a syllable or on the last consonant of an initial consonant cluster.
3. Vowels associated with consonants are nonsequential: they can be located before, after, above or below their associated consonant, or in a combination of these positions.