DMZ 1.7.1 (DataMapper OverZealous Edition)

[eluser]OverZealous[/eluser]
@Alface

It's in the manual. There are 3 ways:

You can set an error using error_message, and not returning anything. (If there are any errors after validating, then the validation has failed.)

Alternatively, you can return a custom string from the validation. Any string value returned is assumed to be an error.

Finally, you can return FALSE, and DMZ will automatically look up the error from a language line based on the name of the validation rule.

Again, these are all explained exactly like this in the manual!