selectCandidate example

    // Determine the still needed plain tags, the still needed attributes, and     // the union of both.     $still_needed_plain_tags = $needed->extractPlainTagsSubset()->diff($provided_plain_tags);
    $still_needed_attributes = $needed->diff($provided)->diff($still_needed_plain_tags);
    $still_needed = $still_needed_plain_tags->merge($still_needed_attributes);

    if (!$still_needed->allowsNothing()) {
      // Select plugins for supporting the still needed plain tags.       $plugin_candidates_plain_tags = self::getCandidates($provided_plain_tags, $still_needed_plain_tags, $disabled_definitions);
      $selected_plugins_plain_tags = self::selectCandidate($plugin_candidates_plain_tags, $still_needed_plain_tags, array_keys($provided_plain_tags->getAllowedElements()));

      // Select plugins for supporting the still needed attributes.       $plugin_candidates_attributes = self::getCandidates($provided, $still_needed_attributes, $disabled_definitions);
      $selected_plugins_attributes = self::selectCandidate($plugin_candidates_attributes, $still_needed, array_keys($provided->getAllowedElements()));

      // Combine the selection.       $selected_plugins = array_merge_recursive($selected_plugins_plain_tags, $selected_plugins_attributes);

      // If additional plugins need to be enabled to support attribute config,       // loop through the list to enable the plugins and build a UI message that       // will convey this plugin-enabling to the user.