Here is a list of predefined validators. You cannot use these names for your custom validators.

name	arguments	task
email		Checks if value is valid email.
notblank		Checks if value is not blank.
notnull		Checks if value is not null.
country		Checks if value is valid country code.
ip		Checks if value is valid internet protocol address.
htmlcolor		Checks if value is valid html color.
nospace		Checks if value has no space chars.
range	[min, max]	Checks if value is in range specified by arguments.
unique		Checks if value is unique in its database table.
regexp	[expression]	Checks if value matches a given regexp.