code: function isDefaultPlugin(name, version) {
      if (!_.contains(DEFAULT_PLUGINS, name)) return false;
  
      try {
          var pluginPkg = require('gitbook-plugin-'+name+'/package.json');
          return semver.satisfies(pluginPkg.version, version || '*');
      } catch(e) {
          return false;
      }
  }
docs: Check if a plugin is a default plugin Plugin should be in the list And version from book.json specified for this plugin should be satisfied