ArgumentType: keyof BaseArgumentType | (string | string[])[] | RegExp | string

The type that the argument should be cast to.

An array of strings can be used to restrict input to only those strings, case insensitive. The array can also contain an inner array of strings, for aliases. If so, the first entry of the array will be used as the final argument.

A regular expression can also be used. The evaluated argument will be an object containing the match and matches if global.