+ /* the route may be a member of a group that has shared-solo
+ * semantics. If so, then all members of that group should follow the
+ * solo of the changed route. But ... this is optional, controlled by a
+ * Controllable::GroupControlDisposition.
+ *
+ * The first argument to the signal that this method is connected to is the
+ * GroupControlDisposition value that was used to change solo.
+ *
+ * If the solo change was done with group semantics (either InverseGroup
+ * (force the entire group to change even if the group shared solo is
+ * disabled) or UseGroup (use the group, which may or may not have the
+ * shared solo property enabled)) then as we propagate the change to
+ * the entire session we should IGNORE THE GROUP that the changed route
+ * belongs to.
+ */
+