boolean isGroupSummary() {
        return options.optBoolean("androidGroupSummary", false);
    }
Set this notification to be the group summary for a group of notifications.
Grouped notifications may display in a cluster or stack on devices which
support such rendering. Requires a group key also be set using setGroup(String).
The group summary may be suppressed if too few notifications are included in the group.

Defaults to false if not set.
src/android/Options.java