encodePluginId example

  protected function getDerivatives(array $base_plugin_definitions) {
    $plugin_definitions = [];
    foreach ($base_plugin_definitions as $base_plugin_id => $plugin_definition) {
      $deriver = $this->getDeriver($base_plugin_id, $plugin_definition);
      if ($deriver) {
        $derivative_definitions = $deriver->getDerivativeDefinitions($plugin_definition);
        foreach ($derivative_definitions as $derivative_id => $derivative_definition) {
          $plugin_id = $this->encodePluginId($base_plugin_id, $derivative_id);
          // Use this definition as defaults if a plugin already defined           // itself as this derivative.           if ($derivative_id && isset($base_plugin_definitions[$plugin_id])) {
            $derivative_definition = $this->mergeDerivativeDefinition($base_plugin_definitions[$plugin_id], $derivative_definition);
          }
          $plugin_definitions[$plugin_id] = $derivative_definition;
        }
      }
      // If a plugin already defined itself as a derivative it might already       // be merged into the definitions.       elseif (!isset($plugin_definitions[$base_plugin_id])) {