diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -62,6 +62,12 @@
 -- > myTransf = rotateBy (1/27)
 ```
 
+In this case, `mySquare` has type `Diagram SVG R2`.  Additionally, you
+may give identifiers of type `IO (Diagram SVG R2)`; in that case the
+`IO` action will be run to determine the diagram to render.  This can
+be useful, for example, when producing a diagram built from some
+external data or using randomness.
+
 You can choose to have the code block included in the Haddock output
 or not, simply by putting it in a Haddock comment or not.  Note that
 the code block defining `mySquare` can be anywhere in the same file;
diff --git a/diagrams-haddock.cabal b/diagrams-haddock.cabal
--- a/diagrams-haddock.cabal
+++ b/diagrams-haddock.cabal
@@ -1,5 +1,5 @@
 name:                diagrams-haddock
-version:             0.2.1.3
+version:             0.2.1.4
 synopsis:            Preprocessor for embedding diagrams in Haddock documentation
 description:         diagrams-haddock is a tool for compiling embedded inline
                      diagrams code in Haddock documentation, for an
@@ -44,7 +44,7 @@
                        parsec >= 3,
                        haskell-src-exts >= 1.14 && < 1.15,
                        blaze-svg >= 0.3 && < 0.4,
-                       diagrams-builder >= 0.3 && < 0.5,
+                       diagrams-builder >= 0.4.2 && < 0.5,
                        diagrams-lib >= 0.6 && < 1.1,
                        diagrams-svg >= 0.8.0.1 && < 1.1,
                        vector-space >= 0.8 && < 0.9,