diff --git a/hierarchy.go b/hierarchy.go
index 0c3b895..f004934 100644
--- a/hierarchy.go
+++ b/hierarchy.go
@@ -11,7 +11,8 @@ type DirectoryHierarchy struct {
 	Entries []Entry
 }
 
-// WriteTo simplifies the output of the resulting hierarchy spec
+// WriteTo simplifies the output of the resulting hierarchy spec.
+// Satisfies the `io.WriterTo` interface.
 func (dh DirectoryHierarchy) WriteTo(w io.Writer) (n int64, err error) {
 	sort.Sort(byPos(dh.Entries))
 	var sum int64