Set of messages (either strings or functions) which will be shown when given validation rule fails. By setting already existing key the appropriate built-in message will be overridden.

$("#myform").kendoValidator({
     rules: {
         custom: function(input) {
            //...
         }
     },
     messages: {
         custom: "Please enter valid value for my custom rule",// defines message for the 'custom' validation rule
         required: "My custom required message", // overrides the built-in message for required rule
         email: function(input) { // overrides the built-in email rule message with a custom function which return the actual message
             return getMessage(input);
         }
     }
});

Set of validation rules. Those rules will extend the built-in ones.

$("#myform").kendoValidator({
     rules: {
         custom: function(input) {
             return input.is("[name=firstname]") && input.val() === "Tom"; // Only Tom will be a valid value for FirstName input
         }
     }
});

Determines if validation will be triggered when element loses focus. Default value is true.