code: public function appendToCollection(array $data)
      {
          list($data) = $this->fireEvent('append-to-collection', [ $data ]);
  
          $files = [];
  
          if(isset($data['files']['js']) && is_array($data['files']['js']))
              $files['js'] = $this->resolveFilesList($data['files']['js'], isset($data['revision']) ? $data['revision'] : null);
          if(isset($data['files']['css']) && is_array($data['files']['css']))
              $files['css'] = $this->resolveFilesList($data['files']['css'], isset($data['revision']) ? $data['revision'] : null);
  
          $this->collection[] = [
              'order'    => isset($data['order']) ? $data['order'] : 0,
              'name'     => isset($data['name'])  ? $data['name']  : uniqid(),
              'files'    => $files,
              'group'    => isset($data['group']) ? $data['group'] : $this->defaultGroup,
              'require'  => isset($data['require']) ? $data['require'] : []
          ];
  
          return $this;
      }
docs: Append asset array to collection. before this, apply required
  indexes if not exists.
  @param  array $asset $array with asset data.
  @return self