Another new feature supporting the WPF-Silverlight continuum
is the VisualStateManager, which introduces a simple new way to apply visual
states to controls. This mechanism provides a way to easily customize both the
look and feel of a control by providing the means to map the control logic to
its respective start and end visual states.
VSM is very flexible in that it automatically generates the
transition animations in between the respective states, so the control author
spends less time writing code and more time on the visual states that are
defined in a control template. That means VSM can give a control author the
ability to easily interchange the look and feel of controls, and VSM gives the
control author a way to easily interchange how a control visually responds to
user interaction. This is fully supported with Expression Blend.