The Work Item Tracking Custom Controls mechanism provides a standard way to enhance T:Microsoft.TeamFoundation.WorkItemTracking.Client.WorkItems to include enhanced user-interface capabilities, extended event-based rules, and workflow capabilities. These custom controls can be bound to T:Microsoft.TeamFoundation.WorkItemTracking.Client.Fields within T:Microsoft.TeamFoundation.WorkItemTracking.Client.WorkItems. These custom controls enable users to view and edit data.
In addition, you'll also find some draft documentation on QueryMergesWIthDetails, which provides more detailed information than the existing QueryMerges method (Merge History).
New APIs now provide the information from the server that you need to build tools to track the flow of changes through branches. This was not possible with the QueryMerges method. The QueryMerges method provided summary merge history information that could only approximate the merge history. SP1 includes a new object model API that gives you the detailed information. The new QueryMergesWithDetails method is in the Microsoft.TeamFoundation.VersionControl.Client namespace.
From: Merge History