Hi,
Added note:
/a(.+?)ter/
You can of course put anything you like there instead of "a" and "ter" (as you already knew) however there are a certain amount of characters that you cant use before escaping them. Without going into much detail, some characters like . ? + * etc. have a special meaning in a regular expression, so they need to be escaped. In other words if you wanted to get pieces of text that are in between: . and + you would have to escape them by putting a backslash \ in front of them. Some more chars have to be escaped, because of the way mirc's identifiers work.
This is a non-exhaustive list of characters that you should escape: . + ? * ( ) , [ ] ^ $ / \
Examples:
Between . and * --> / \.(.+?)\*/
Between + and ? --> /\+(.+?)\?/
Between ( and ) --> /\((.+?)\)/
Between [ and ] --> /\[(.+?)\]/
...
There a few possible solutions for your request, and the one I gave you is one of them. If you escape those special chars (if u should need them), then it will work fine.
Greets