DUNION=0 Common edges always shown
All common edges between adjoining elements will be drawn in DRAFT.
DUNION=1 Common edges not shown between members
Common edges between adjoining elements will be drawn in DRAFT unless a pair of
such elements are both members of a common parent, in which case the edge lines
will be removed.
DUNION=2 Common edges not shown between members and peers
Common edges between adjoining elements will be drawn in DRAFT unless a pair of
such elements are either both members of a common owner or are at the same
hierarchic level with a common parent, in which cases the edge lines will be removed.
