TActiveCustomValidator
API Manual
Performs custom validation using only server-side OnServerValidate
validation event. The client-side uses callbacks to raise
onServerValidate event. The ClientValidationFunction property
is disabled and will throw an exception if trying to set this property.
Beware that the onServerValidate may be
raised when the control to validate on the client side
changes value, that is, the server validation may be called many times.
After the callback or postback, the {@link onServerValidate onServerValidate}
is raised once more. The IsCallback property of the TPage class
will be true when validation is made during a callback request.