I wonder why they did it - perhaps they were trying to avoid having digraphs mapping to a single sound. An alternative might be carons + acute accents to modify

I wonder why they did it - perhaps they were trying to avoid having digraphs mapping to a single sound. An alternative might be carons + acute accents to modify the letter like the Czech, Slovak and in the Balkans so in the example from the article below... > Under this new system, the Kazakh word for cherry will be written as s’i’i’e, and pronounced she-ee-ye. You could define the alphabet so that this is written "šííě". To be honest it seems like this is a tricky example to map to any latin-based alphabet. Maybe diacritics were avoided to avoid internationalisation issues (i.e. you could easily fall back to the locale "en-us" and your Kazakh doc still looks alright)