protected function _cloneActiveContext($active_ctx) {
    $child = new stdClass();
    $child->{'@base'} = $active_ctx->{'@base'};
    $child->mappings = self::copy($active_ctx->mappings);
    $child->inverse = null;
    if(property_exists($active_ctx, '@language')) {
      $child->{'@language'} = $active_ctx->{'@language'};
    }
    if(property_exists($active_ctx, '@vocab')) {
      $child->{'@vocab'} = $active_ctx->{'@vocab'};
    }
    return $child;
  }