A child of 'group' is used for clipping it. This item must be stored inside a variable in order to reuse it for the clipping code.
Example 3.31. ::vgcode::dump-configure-Zinc using clipzinc
...
# with this item (should be the parent group).
set clippedGroup \
[groupOf $target $_clip($id)]
append _graphics \
[dumper::clipzinc $ta_name $type $id $group $clippedGroup $coords $properties $transformation]