diff --git a/tags.go b/tags.go
index c00685b..57edabd 100644
--- a/tags.go
+++ b/tags.go
@@ -1,6 +1,7 @@
 package gomatrix
 
 // Tag contains the data for an m.tag message type
+// https://matrix.org/docs/spec/client_server/r0.4.0.html#m-tag
 type Tag struct {
 	Tags map[string]TagProperties `json:"tags"`
 }