code: func FilterConfiguringFilter(c *Controller, fc []Filter) {
  	if newChain := getOverrideChain(c.Name, c.Action); newChain != nil {
  		newChain[0](c, newChain[1:])
  		return
  	}
  	fc[0](c, fc[1:])
  }
docs: // FilterConfiguringFilter is a filter stage that customizes the remaining
  // filter chain for the action being invoked.