code: func run(c *Context, m, n []Middleware, h Handler) {
  	switch {
  	case len(m) > 0:
  		if m[0] != nil {
  			m[0](c, func(ctx *Context) { run(ctx, m[1:], n, h) })
  		} else {
  			run(c, m[1:], n, h)
  		}
  	case len(n) > 0:
  		if n[0] != nil {
  			n[0](c, func(ctx *Context) { run(ctx, nil, n[1:], h) })
  		} else {
  			run(c, nil, n[1:], h)
  		}
  	case h != nil:
  		h(c)
  	}
  }
docs: // run executes the middleware chains m and n and the handler h using
  // c as the initial context. If a middleware or handler is nil, run
  // simply advances to the next middleware or handler.