diff --git a/packages/flutter/lib/theme/README.md b/packages/flutter/lib/theme/README.md
new file mode 100644
index 0000000000..ba58170807
--- /dev/null
+++ b/packages/flutter/lib/theme/README.md
@@ -0,0 +1,5 @@
+This directory provides constants for Material Design.
+
+   http://www.google.com/design/spec/material-design/
+
+Files in this directory only depend on ../painting/* and sky:dart.
diff --git a/packages/flutter/lib/theme/edges.dart b/packages/flutter/lib/theme/edges.dart
index 4da5d9b44e..fad0e0f09d 100644
--- a/packages/flutter/lib/theme/edges.dart
+++ b/packages/flutter/lib/theme/edges.dart
@@ -4,6 +4,7 @@
 
 enum MaterialEdge { canvas, card, circle }
 
+// This map gives the border radii for each type of material.
 const Map<MaterialEdge, double> edges = const {
   MaterialEdge.canvas: null,
   MaterialEdge.card: 2.0,