Validators are designed to take some input data, check it for correctness, and return a boolean result telling whether the data is correct (and error messages if the data has some errors).
In Zend Framework 3, there are several groups of standard validators:
In some cases, a standard validator is not suitable, and you need to apply your own checking
algorithm to the input data. In such case, you may use either the
Callback validator or
write your own custom validator class.