VSTS2010 Addin Development - Check-in hooks

I've been tipping my toes in Visual Studio Add-In development. I've read some of the tutorials online, and studied some of the sample code provided. Now I actually want to perform custom actions before/after a TFS check-in command is called by the user, but I can't seem to figure out where I can find a hook to start this.

Is there something开发者_如何学C like that available in the SDK? Can someone point me in the right direction?

Thanks a lot!

Roel

Edit:

The use of check-in policy is not gonna help me in my situation. I want to show dialogs before and/or after the check-in command is invoked. Even (if it is possible) to alter the existing check-in dialog.

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Here is a good article on the subject: http://blogs.msdn.com/jimlamb/archive/2010/03/31/how-to-implement-package-and-deploy-custom-check-in-policy-for-tfs-2010.aspx