Applies to : ZWCAD Classic; ZWCAD+ 2015
XFADECTL: This is to control the other objects that are out of the in-place editing xref or block, like below figure shown.
Attached is a video to show how it works.
The XREF is marked by red rectangle.
XDWGFADECTL: This is to control the XREF fade level compared with other objects in the drawing, not in the in-place editing case. This system variable is not supported in ZWCAD+.