Let's say that your validation is conditional on multiple rules.... This is a bit tricky because it's not obvious how to get the other rules passed to the validator. Here's how you'd do it
Validator::extend('combined_under_3', function ($attribute, $value, $parameters, $validator)
{
//this will return all rules with values passed to this validator instance!
$allValues = $validator->getData();
$total = $attribute + $allValues['second-value'];
return $total < 3;
});
//also, don't forget to add a custom validation message!