code: public static void addInputMap(Node node, InputMap<?> im) {
          // getInputMap calls init, so can use unsafe setter
          setInputMapUnsafe(node, InputMap.sequence(im, getInputMap(node)));
      }
docs: Adds the given input map to the start of the node's list of input maps, so that an event will be pattern-matched
  against the given input map before being pattern-matched against any other input maps currently
  "installed" in the node.