[pavlov]

In the case of a delete action in a text editor, are you sure that deleting the whole grapheme is actually what the Tamil or Korean user wants?

You mentioned the following examples in your grandparent post:

- 'நி' (Tamil letter NA + Tamil Vowel Sign I)

- Hangul made of conjoining Jamo (such as '깍': 'ᄁ' + 'ᅡ' + 'ᆨ')

I don't speak either language, but it doesn't seem unreasonable to me that pressing Delete would delete just the vowel sign in Tamil, or just the last component within the Hangul character. In fact, that might be just what the user wants?

[taejo]

> I don't speak either language, but it doesn't seem unreasonable to me that pressing Delete would delete just the vowel sign in Tamil, or just the last component within the Hangul character. In fact, that might be just what the user wants?

My Korean is pretty poor, but I think that's exactly what one wants. If you mistype a letter, you want to retype that letter, not the whole syllable. However, this should work uniformly: it shouldn't matter if the syllable is represented as a single codepoint or made up of comjoining jamo.

[yew]

If the Hangul and Tamil constructs are anything like ligatures (e.g. fi in the Latin alphabet), I would imagine that's the case most of the time. Plus lots of special rules for which glyphs to treat as single symbols and which to decompose (e.g. & is technically a ligature but almost never decomposed).

[btn]

are you sure that deleting the whole grapheme is actually what the Tamil or Korean user wants?

I'm not, but I think it's the only sane thing for a text editor to do if you don't want it to incorporate a ton of language-specific rules. The UAX actually does make a distinction between "legacy" and "extended" grapheme clusters---if you're handing "delete", you'll want to use "legacy clusters" to separate the two Tamil marks; but for text selection, use "extended clusters" will combine them (it's a little bit more complicated than that, but there are properties of Unicode that allow you to handle the "preferred" method for editing a script, while remaining mostly language-agnostic).

Hangul is trickier, but input happens through an IME that "composes" the characters before they are committed to the editor. The IME will perform component-wise deletion, but once it's committed, the editor will operate on the grapheme. It's not a perfect solution, but keeping the composition/decomposition rules for the language in the IME seems preferable.