code: func IPv6Fragment(checkers ...NetworkChecker) NetworkChecker {
  	return func(t *testing.T, h []header.Network) {
  		t.Helper()
  
  		if p := h[0].TransportProtocol(); p != header.IPv6FragmentHeader {
  			t.Errorf("Bad protocol, got %v, want %v", p, header.UDPProtocolNumber)
  		}
  
  		ipv6Frag := header.IPv6Fragment(h[0].Payload())
  		if !ipv6Frag.IsValid() {
  			t.Error("Not a valid IPv6 fragment")
  		}
  
  		for _, f := range checkers {
  			f(t, []header.Network{h[0], ipv6Frag})
  		}
  		if t.Failed() {
  			t.FailNow()
  		}
  	}
  }
docs: // IPv6Fragment creates a checker that validates an IPv6 fragment.