ISO 11940 - Character Sequencing

Character Sequencing

In general characters are transliterated from left to right and, where characters have the same horizontal position, from top to bottom. The vertical sequencing is in fact simply specified as tone marks and thanthakhat (–์) preceding any other marks above or below the consonant. The standard denies at the end of Section 4.2 that the combination of sara u (◌ุ, ◌ู) and nikkhahit (◌ํ) can occur and then gives an example of it when specifying the transliteration of nikkhahit, but does not show the transliteration of the combination. The effect of these rules is that, except for nikkhahit, all the non-vowel marks attached to a consonant in Thai are attached to the consonant in the Roman transliteration.

The standard concedes that attempting to transpose preposed vowels and consonants may be comforting to those used to the Roman alphabet, but recommends that preposed vowels not be transposed.

For example, ภาษาไทย (RTGS: Phasa Thai) should be transliterated to p̣hās̛̄āịthy and เชียงใหม่ (RTGS: Chiang Mai) to echīyngıh̄m̀.