It is very useful to be able to use Unicode expressions for character matching, and many engines can do it, but Nova’s JS engine can’t.
For example, I’d like to be able to use the following expression to match C identifiers:
/^[\p{XID_Start}][\p{XID_CONTINUE}]$/
(Btw, I expect this to be useful for more programming languages than just C. Unicode TR31 is aimed at making it easier for languages to future-proof for Unicode standards.)
Even a simpler form, /\p{L}/ does not seem to work.