Indicates the type of validator to use. Recognised type values are:
- string: Must be of type string. This is the default type.
- number: Must be of type number.
- boolean: Must be of type boolean.
- method: Must be of type function.
- regexp: Must be an instance of RegExp or a string that does not generate an exception when creating a new RegExp.
- integer: Must be of type number and an integer.
- float: Must be of type number and a floating point number.
- array: Must be an array as determined by Array.isArray.
- object: Must be of type object and not Array.isArray.
- enum: Value must exist in the enum.
- date: Value must be valid as determined by Date
- url: Must be of type url.
- hex: Must be of type hex.
- email: Must be of type email.
- any: Can be any type.