Adobe After Effects CS3 - Manual (Page 237)

AFTER EFFECTS CS3
User Guide
232
Overlap pin with positive In Front value (top), and Overlap pin with negative In Front value (bottom)
Each Overlap pin has the following properties:
In Front The apparent proximity to the viewer. The influence of Overlap pins is cumulative, meaning that the In
Front values are added together for places on the mesh where extents overlap. You can use negative In Front values
to cancel out the influence of another Overlap pin at a specific location.
Extent How far from the Overlap pin its influence extends. The influence ends abruptly; it does not decrease
gradually with distance from the pin. Extent is indicated visually by a fill in the affected parts of the mesh. The fill is
dark if In Front is negative; the fill is light if In Front is positive.
Puppet Starch controls
When you are distorting one part of an image, you may want to prevent other parts from being distorted. For
example, you may want to preserve the rigidity of an arm as you move a hand to make it wave. Use the Puppet Starch
tool to apply Starch pins to the part of an object that you want to keep rigid.
You apply Puppet Starch pins to the original outline, not to the deformed image.