code: function queryComponentInstance(ctx, id) {
      let isSelectAll = Array.isArray(id);
      isSelectAll && (id = id[0]);
  
      // query multiple components is not supported
      let key = id.substr(1);
      return ctx.$child(key);
  }
docs: Query component instance by the given id
  
  @inner
  @param {Object} ctx the component context
  @param {string} id the component reference id
  @return {?Object}