Why ASP.NET MVC 2 will have its own client-side validation?

I am interested what are possible reasons that ASP.NET M开发者_运维问答VC 2 will have its own client-side validation instead of merging with xVal validation framework? Has someone from ASP.NET MVC team blogged about it?

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They are providing a way to plug in some other library for client-side validation.

Haacked blog:

Client-Side Validation – ASP.NET MVC 2 includes the jQuery validation library to provide client-side validation based on the model’s validation metadata. It is possible to hook in alternative client-side validation libraries by writing an adapter which adapts the client library to the JSON metadata in a manner similar to the xVal validation framework.