diff --git a/limmutable.c b/limmutable.c
index 4f9d80d..a12e324 100644
--- a/limmutable.c
+++ b/limmutable.c
@@ -13,6 +13,13 @@
 *     assert(foo.class_var == 5)
 * 
 * Instances *are* garbage collected.
+*
+* Class layout:
+*     __instances: weak-valued map from hash -> hash bucket
+*         hash buckets: weak-keyed map from instance userdata -> table of values
+*     __buckets: weak-keyed map from instance userdata -> hash bucket (used to manage hash bucket lifetimes)
+*     __fields: list of named fields
+*     __indices: map from field names to the index in the instance table where the value is stored
 */
 
 #include "lua.h"