/**
 * Get a new key->node mapping
 * 
 * @param {String|Number} key
 * @param {Object|Array|String|Number|null} node a value found in the json
 */
function namedNode(key, node) {
   return {key:key, node:node};
}

/** get the key of a namedNode */
var keyOf = attr('key');

/** get the node from a namedNode */
var nodeOf = attr('node');