Use new Tag type for slice separator.

build.go

@@ -118,6 +118,7 @@ func buildNode(v reflect.Value, seenFlags map[string]bool, cmd bool) *Node {
 				Help:    tag.Help,
 				Default: tag.Default,
 				Decoder: decoder,
+				Tag:     tag,
 				Value:   fv,
 
 				// Flags are optional by default, and args are required by default.

decoders.go

@@ -222,7 +222,7 @@ func floatDecoder(bits int) DecoderFunc {
 
 func sliceDecoder(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 	el := target.Type().Elem()
-	sep, ok := ctx.Value.Tag.Lookup("sep")
+	sep, ok := ctx.Value.Tag.Get("sep")
 	if !ok {
 		sep = ","
 	}

model.go

@@ -30,7 +30,7 @@ type Value struct {
 	Help     string
 	Default  string
 	Decoder  Decoder
-	Tag      reflect.StructTag
+	Tag      *Tag
 	Value    reflect.Value
 	Required bool
 	Set      bool   // Used with Required to test if a value has been given.

tag.go

@@ -123,8 +123,9 @@ func (t *Tag) Has(k string) bool {
 	return ok
 }
 
-func (t *Tag) Get(k string) (string, error) {
-	return t.items[k], nil
+func (t *Tag) Get(k string) (string, bool) {
+	s, ok := t.items[k]
+	return s, ok
 }
 
 func (t *Tag) GetBool(k string) (bool, error) {