In terms of script classification, Pahawh Hmong is something of an anomaly. It is written from left to right, and generally, consonants and vowels are both written with full letters. The language is largely monosyllabic, each syllable consisting of a consonant followed by a vowel with inherent tone (the 'rime' of the syllable). However, it is written in such a way that the rime is primary, and the consonant secondary, so each syllable has to be read "backwards" - that is from right to left - in order to be pronounced correctly. This is unique amongst the world's documented writing systems. Additionally, syllable-final [ŋ] and syllable-initial [k] are considered to be inherent in a vowel where no other consonant is written, but mid-tone [au] is also inherent in a consonant. So, in the syllable 'kau', one of the inherent elements must be written, and it is the vowel [au]. This, along with the rime-initial order in which syllables are written, indicates that the vowel is the basic unit in the script.
In the strict sense of the word, it cannot be called an abugida as it is non-segmental; consonant clusters and vowels with inherent final consonants are represented with a single symbol. However, some linguists do classify it as a vowel-based abugida because it is based on vowels with consonant notation as obligatory but secondary. Others analyze syllable-final [ŋ] as vowel nasalization, and classify the script as a non-segmental alphabet like the Latin script, which represents complex sounds such as [ks] and [ai] with the single symbols 'x' and 'i'.