What do `?i` and `?-i` in regex mean?

Question

Could someone explain what (?i) and (?-i) wrapping a word in regex mean?

(?i)test(?-i)

I tested and it matches

Answer 1

(?i) turns on case-insensitive mode, (?-i) turns it off.

For example, if you tried (?i)te(?-i)st, it would match test, TEst, tEst, but not teST.