Sub-expression or capture group: (foo)

Named capture group: (?<name>foo)

Non-capturing group: (?:foo)

Lookahead: (?=foo)

For negative lookahead, change = to !: (?!foo)

For lookbehind, add <: (?<=foo)

For negative lookbehind, change = to !: (?<!foo)

(Not from memory, had to look everything up...)