Metacharacters:
    [ ] \ ^ $ . | ? * + ( )
    { } // only if after character class

Character classes:
    [] match a single character
    /gr[ae]y/ will match gray or grey
    - (hyphen) is a range, e.g. [a-z]
    ^ (caret) is a NOT whcih negates whole class, e.g. [^f]