[1] The Yale system places primary emphasis on showing a word's morphophonemic structure.
In terms of morphophonemic content, the Yale system's approach can be compared to North Korea's former New Korean Orthography.
It is also used for other purposes such as to indicate sound change:[11] A macron over a vowel letter indicate that in old or dialectal language, this vowel is pronounced long:[12] Accents marks are used instead of or in addition to the macron when recording dialects, such as Gyeongsang or Hamgyeong, which have retained tones.
A superscript letter indicates consonants that have disappeared from a word's South Korean orthography and standard pronunciation.
If used for modern day language, this just means the symbol e⁄a, though Middle Korean also had the vowel alternation u⁄o.