fix required/xor behavior w/ > 2 flags

context.go

@@ -793,8 +793,8 @@ func checkMissingFlags(flags []*Flag) error {
 			missing = append(missing, flag.Summary())
 		}
 	}
-	for _, flags := range xorGroup {
+	for xor, flags := range xorGroup {
-		if len(flags) > 1 {
+		if !xorGroupSet[xor] && len(flags) > 1 {
 			missing = append(missing, strings.Join(flags, " or "))
 		}
 	}

kong_test.go

@@ -932,6 +932,10 @@ func TestXorRequiredMany(t *testing.T) {
 	_, err := p.Parse([]string{"--one"})
 	require.NoError(t, err)
 
+	p = mustNew(t, &cli)
+	_, err = p.Parse([]string{"--three"})
+	require.NoError(t, err)
+
 	p = mustNew(t, &cli)
 	_, err = p.Parse([]string{})
 	require.EqualError(t, err, "missing flags: --one or --two or --three")