With these changes, sway will respect positive exclusive zones of layer
surfaces anchored to one or three sides.
This matches the protocol, which states that a positive exclusive zone
should be respected, "if the surface is anchored to one edge or an
edge and both perpendicular edges". If the surfaces is "anchored to
only two perpendicular edges (a corner), anchored to only two
parallel edges or anchored to all edges a positive value will be
treated the same as zero".
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