code: function getPropWalkFn(descriptor) {
    var parts = descriptor.split(/ ?\[\]/);
    if (parts.length === 2) {
      return mapProp.bind(null, parts[0]);
    }
    return getProp.bind(null, descriptor);
  }
docs: Returns a function that will walk a single property of a node. `descriptor` is a string indicating the property name, optionally ending with '[]' (e.g., 'children[]').