code: func extractHandlerContext(handler Handler) ([]interface{}, Handler) {
  	var kvs []interface{}
  
  	if c, ok := handler.(*contextualHandler); ok {
  		handler = c.handler
  		kvs = c.keyvals
  	}
  
  	return kvs, handler
  }
docs: // extractHandlerContext extracts the context and optionally the wrapped handler when it's the same container.