$when public property A PHP callable whose return value determines

$skipOnEmpty public property Whether this validation rule should

validateAttribute() public method Validates a single attribute

$attributes public property Attributes to be validated by this

clientValidateAttribute() public method Returns the JavaScript

$builtInValidators public static property List of built-in validators

addError() public method Adds an error about the specified

validateValue() protected method Validates a value.

isActive() public method Returns a value indicating whether

isEmpty() public method Checks if the given value is empty