Store the name of the class.
Default form field.
A form field is providing a defined set of methods and properties to be used in the rendering of the fields in forms, in the conversion of the data from the user input to a form usable by the models.
multiClean( $value) : array
Multi-clean a value.
If you are getting multiple values, you need to go through all of them and validate them against the requirements. This will do that for you. Basically, it is cloning the field, marking it as not multiple and validate each value. It will throw an exception in case of failure.
If you are implementing your own field which could be filled by a "multiple" widget, you need to perform a check on $this->multiple.