diff --git a/semantic-tags/src/AST/Element.hs b/semantic-tags/src/AST/Element.hs
index 2157d6f9c..50b6d2535 100644
--- a/semantic-tags/src/AST/Element.hs
+++ b/semantic-tags/src/AST/Element.hs
@@ -16,6 +16,7 @@ instance (Element' side sub sup, side ~ Find sub sup) => Element sub sup where
   prj = prj' @side
 
 
+-- | A pattern synonym to conveniently project out matching elements.
 pattern Prj :: Element sub sup => sub a -> sup a
 pattern Prj sub <- (prj -> Just sub)