diff --git a/docs/source/overview.rst b/docs/source/overview.rst
index 5f40e43..118c9b7 100644
--- a/docs/source/overview.rst
+++ b/docs/source/overview.rst
@@ -6,7 +6,7 @@ to describe in-situ structured data without requiring transformation
 into a canonical form.
 
 Similar to NumPy, datashape includes ``shape`` and ``dtype``, but combined
-together in the type system. 
+together in the type system.
 
 Units
 -----
@@ -186,6 +186,12 @@ can be written as two free type vars::
 
     A * B * int32
 
+.. note::
+
+   Any name beginning with an uppercase letter is parsed as a symbolic type
+   (as opposed to concrete). Symbolic types can be used both as dimensions and
+   as data types.
+
 Option
 ~~~~~~