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.

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