Adobe After Effects - Manual (Page 262)

In Front
Extent
To the top
Amount
Overlap pin with negative In Front value (top), and Overlap pin with positive In Front value (bottom)
Each Overlap pin has the following properties:
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.
An area of the mesh that is not influenced by Overlap pins has an implicit In Front value of 0. The default value for a new Overlap pin is 50.
When animating the In Front value, you should usually use Hold keyframes. You do not usually want to interpolate gradually from an element
being in front to an element being in back.
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.
Unwanted distortion in figure (upper left) is prevented with Starch pin (upper right and lower left)
Each Starch pin has the following properties:
The strength of the stiffening agent. The influence of Starch pins is cumulative, meaning that the Amount values are added together for
places on the mesh where extents overlap. You can use negative Amount values to cancel out the influence of another Starch pin at a specific
location.
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