diff --git a/Graphics/Diagrams/Core.hs b/Graphics/Diagrams/Core.hs
--- a/Graphics/Diagrams/Core.hs
+++ b/Graphics/Diagrams/Core.hs
@@ -70,6 +70,8 @@
   recip = fmap recip
   (/) = liftA2 (/)
 instance AbelianAdditive x => AbelianAdditive (R env x)
+instance Ring x => Module (R env x) (R env x) where
+  (*^) = (*)
 instance Ring x => Ring (R env x) where
   fromInteger x = pure (fromInteger x)
 instance Field x => Field (R env x) where
@@ -298,6 +300,8 @@
   zero = S "0"
 instance AbelianAdditive (SExpr)
 instance Field (SExpr)
+instance Module SExpr SExpr where
+  (*^) = (*)
 instance Ring (SExpr)
 instance Group (SExpr) where
   negate = unop "-"
diff --git a/Graphics/Diagrams/Types.hs b/Graphics/Diagrams/Types.hs
--- a/Graphics/Diagrams/Types.hs
+++ b/Graphics/Diagrams/Types.hs
@@ -145,8 +145,8 @@
                                                  (location -> (FrozenPoint -> m ()) -> x ()) -> -- freezer
                                                  (forall a. m a -> x a) -> -- embedder
                                                  location ->
-                                                 lab -> -- label specification
-                                                 x BoxSpec
+                                                 lab -> -- label specification (eg. the text; backend-dependent)
+                                                 x BoxSpec -- the backend returns the size of the label
                          }
 
 tracePath :: Lens' (Backend lab m) (PathOptions -> FrozenPath -> m ())
diff --git a/lp-diagrams.cabal b/lp-diagrams.cabal
--- a/lp-diagrams.cabal
+++ b/lp-diagrams.cabal
@@ -1,5 +1,6 @@
+cabal-version:       1.18
 name:                lp-diagrams
-version:             2.1.2
+version:             2.1.3
 synopsis:            An EDSL for diagrams based based on linear constraints
 license:             AGPL-3
 license-file:        LICENSE
@@ -9,7 +10,6 @@
 category:            Graphics
 build-type:          Simple
 -- extra-source-files:  
-cabal-version:       >=1.18
 description:
   A library to describe diagrams. The defining
   feature of the package is the ability to use linear constraints to