Rudimentary BMP support, probably. You basically have to account for combining characters and double-width characters. Emojis and multi-character* presentation

Rudimentary BMP support, probably. You basically have to account for combining characters and double-width characters. Emojis and multi-character* presentation form code points like U+FDFD would take a lot more work to do correctly. * I'm using "character" here in the linguistic sense. Unicode did not invent the word "character" and it doesn't only mean code points.