--- a/src/transport_internal.h	Tue Apr 28 23:09:28 2009 +0300
+++ b/src/transport_internal.h	Tue Apr 28 23:10:30 2009 +0300
@@ -53,6 +53,9 @@
  * The definition of a transport type
  */
 struct transport_type {
+    /** Parent type */
+    const struct transport_type *parent;
+
     /** Method table */
     struct transport_methods methods;
 };
@@ -83,7 +86,7 @@
 
 /**
  * Check the type of the transport, and return the transport as a void* suitable for casting to the appropriate struct
- * for the type.
+ * for the type, or any of its children.
  *
  * It is a bug to call this with a transport of a different type.
  */