PreValidate is not called when AutoValidator not defined

I read the docs of prevalidation from this [link](https://granitic.io/ref/validation). It mentions to implement ```WsPreValidateManipulator```. But the PreValidate is not called unless I define ```AutoValidator``` in the handler. I have given the reference to ```PreValidateManipulator``` as well in the handler. Is it the expected behaviour? Am I missing anything.