diff --git a/plugin.go b/plugin.go
index a3ed815..fec7717 100644
--- a/plugin.go
+++ b/plugin.go
@@ -9,8 +9,10 @@ type FuncProvider interface {
 	FuncMap () template.FuncMap
 }
 
-// FuncProviderFor is an object that provides
+// FuncProviderFor is an object that provides a template.FuncMap for a specific
+// document.
 type FuncProviderFor interface {
+	FuncProvider
 	// FuncMap provides a template.FuncMap, given a particular document. It
 	// may return nil, in which case its result is simply not considered.
 	FuncMapFor (*Document) template.FuncMap