static getNodes(context, callback) {
    const Functional = shaka.util.Functional;
    goog.asserts.assert(
        callback(context.representation),
        'There must be at least one element of the given type.',
    );

    return [
      callback(context.representation),
      callback(context.adaptationSet),
      callback(context.period),
    ].filter(Functional.isNotNull);
  }
Parses common attributes for Representation, AdaptationSet, and Period.
@param {shaka.dash.DashParser.Context} context
@param {function(?shaka.dash.DashParser.InheritanceFrame):
   ?shaka.extern.xml.Node} callback
@return {!Array<!shaka.extern.xml.Node>}