private boolean addToFragment(ProgramNode destNode, ProgramNode dropNode) {
		// dropNode can be either fragment or module
		ProgramFragment destFrag = destNode.getFragment();
		try {
		    tree.mergeGroup(dropNode.getGroup(), destFrag);
		    tree.removeSelectionPath(dropNode.getTreePath());
		    return true;
		} catch (Exception e) {
		    Msg.showError(this, null, "Error", "Error Moving Fragments", e);
		}
		return false;
	}
Check whether the drop is ok given that destNode is a fragment.
@param destNode fragment node
@param dropNode node that is getting dropped
@param dropAction move or copy action
@return true if the destNode is a valid drop target
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/programtree/DnDMoveManager.java