When do I need to escape characters within a regex character set (within [])?

Question

Are the rules for what I escape in a bracket different for what I do outside of brackets?

For example should I escape a ? inside a bracket? Is it

Answer 1

The only thing that needs to be escaped in brackets is a closing bracket, and a minus if it is not initial or final, and a hat if it is initial, AFAIK. And the backslash itself, obviously.

The reason is, these are the only characters with a special significance inside the brackets. A closing bracket ends the brackets, a mid-string minus indicates a range, and an initial hat negates the bracket class. Everything else should be literally interpreted. The backslash is the escape character, so you need a double backslash to match a literal backslash.