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entry variable: $selfstilt -- selfintersect stilt
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default: -1.0

The "selfd:" entry (F3 panel, middle bottom)
controls the how far to move along the surface
normal from a vertex before nearest-neighbor
marking the self-intersection volume.

A negative $selfstilt is inward, and a positive
$selfstilt is outward.

Slightly negative (inward) unsticks an
outward-moving surface (and vice versa).

No effect unless $chkselfintflag is TRUE (=1).
