The transliteration system referred to as Cœdès system is a reversible transliteration for Thai and Khmer, developed by Georges Cœdès and published in table form by his student Uraisi Varasarin.
[2] It tends to be favoured over the Royal Thai General System of Transcription—the official scheme promulgated by the Royal Thai Institute—because the latter is not reversible, as it underrepresents vowel quality and quantity.
The Thai script was devised at a stage when the language contrasted three tones.
For a transliteration system that aims at exhaustivity, it seemed useful to have a system that covers all five types of tones, including explicit marking for the absence of tone mark.
The following proposal was put forward by Krisda Tan Sirijunto and Alexis Michaud in 2015.