The new option takes a value indicating which cell types should be
written out as polyhedra. The values are as follows:
none: No polyhedral cells are written. Cells which match specific
shapes (hex, pyramid, prism, ...) are written as their
corresponding VTK cell types. Arbitrary polyhedral cells
that do not match a specific shape are decomposed into
tetrahedra.
polyhedra: Only arbitrary polyhedral cells are written as a VTK
polyhedron. Cells that match specific shapes are written as
their corresponding VTK cell types.
all: All cells are written as a VTK polyhedron.
The default is 'none', which retains the previous default behaviour.
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