diff --git a/semantic-tags/src/AST/Element.hs b/semantic-tags/src/AST/Element.hs
index a0a34e84e..fb691e1e5 100644
--- a/semantic-tags/src/AST/Element.hs
+++ b/semantic-tags/src/AST/Element.hs
@@ -6,6 +6,7 @@ module AST.Element
 import GHC.Generics
 import GHC.TypeLits (ErrorMessage(..), TypeError)
 
+-- | Projection of an element out of a tree of sums, particularly suitable for use with highly branching (e.g. balanced) trees.
 class Element sub sup where
   prj :: sup a -> Maybe (sub a)