code: function getParent(spec_c, className) {
    var parent = getChild(spec_c, 'basecompoundref');
    if (parent) {
      parent = getText(parent);
      if (!_.has(xml2js.CLASSES, parent)) {
        console.log('WARNING: Class ' + className + ' has unknown parent class ' + parent);
      }
    }
    return parent;
  }
docs: get parent class, if any