Rename the folder node type from group to folder, freeing group for the draw option

graph.go

@@ -51,7 +51,7 @@ type namedNode struct {
 
 func contained(n node) []namedNode {
 	switch n := n.(type) {
-	case *group:
+	case *folder:
 		return named(n.children)
 	case *choice:
 		out := make([]namedNode, len(n.items))
@@ -69,7 +69,7 @@ func contained(n node) []namedNode {
 // named skips a bound {/path} key: it is a render edge, not containment, so using
 // it as a path segment would report a node under a path that does not reach it. Only
 // a template's fields hold bindings — loadDir skips a dot-prefixed entry, so a
-// group's children never carry the prefix — so this one skip serves both.
+// folder's children never carry the prefix — so this one skip serves both.
 func named(m map[string]node) []namedNode {
 	out := make([]namedNode, 0, len(m))
 	for _, name := range sortedNames(m) {
@@ -111,7 +111,7 @@ func (e renderEdge) reached() string {
 
 // renderEdges lists the children rendering n recurses into, mirroring expand: a
 // choice's items, and a template's field/reference tokens plus its operands. A
-// group renders nothing, so it has no edges.
+// folder renders nothing, so it has no edges.
 func renderEdges(n node) []renderEdge {
 	switch n := n.(type) {
 	case *choice: