code: func (g *routeGroup) Group(prefix string) IRouteGroup {
  	rg := &routeGroup{
  		prefix:     g.prefix + prefix,
  		lars:       g.lars,
  		middleware: make(HandlersChain, len(g.middleware)),
  	}
  	copy(rg.middleware, g.middleware)
  	return rg
  }
docs: // Group creates a new sub router with specified prefix and retains existing middleware.