Assembly: PresentationFramework (in PresentationFramework.dll)
When the user drags the thumb of a ScrollBar, the ScrollBar calls CanExecute for the . If CanExecute returns true, the ScrollBar executes that command. If CanExecute returns false, the ScrollBar executes the ScrollToVerticalOffsetCommand.
The ScrollViewer uses this command to enable deferred scrolling. When ScrollViewer.IsDeferredScrollingEnabled is true and a user drags the Thumb of the ScrollBar, the content of the ScrollViewer does not change until the user releases the Thumb. If deferred scrolling is enabled, the ScrollBar executes the for a vertical ScrollBar when the user drags the Thumb.