private boolean applyIsSet() {
		if (diffControl == null) {
			return false;
		}
		ProgramMergeFilter filter = diffControl.getMergeFilter();
		// Want to know if something other than the primary symbol filter is set.
		filter.setFilter(ProgramMergeFilter.PRIMARY_SYMBOL, ProgramMergeFilter.IGNORE);
		return filter.isSet();
	}
Callback when user changes selection in the program2 diff panel.

Note: A P2 selection is handed to this method when a selection is made in the diff listing
which displays P2.
Ghidra/Features/ProgramDiff/src/main/java/ghidra/app/plugin/core/diff/ProgramDiffPlugin.java