- [S] means any of a set of characters described by S.

[ S] means any character not described by S.- [abc] is the same as EBNF ("a" | "b" | "c")
- [a-cxyz] is the same as EBNF ("a" | "b" | "c" | "x" | "y" | "z")
- [ xz] matches anything but x or z

- . matches everything but a newline. It is the same as [ n]

- [0-9]+ describes integer numbers.
- "[ "]*" describes simple strings without escapes.