Merge pull request #40 from WebAssembly/tweak-refines-text-format

Tweak text format of refines clause

Author: lukewagner

design/mvp/Binary.md

@@ -215,7 +215,8 @@ Notes:
   names requires that the name be unique for the record, variant, flags, or enum
   type definition.
 * Validation of the optional `refines` clause of a variant case requires that
-  the case index is within bounds for the variant type's cases.
+  the case index is less than the current case's index (and therefore
+  cases are acyclic).
 
 
 ## Canonical Definitions

design/mvp/Explainer.md

@@ -415,7 +415,7 @@ defvaltype    ::= unit
                 | float32 | float64
                 | char | string
                 | (record (field <name> <valtype>)*)
-                | (variant (case <name> <valtype> (refines <name>)?)+)
+                | (variant (case <id>? <name> <valtype> (refines <id>)?)+)
                 | (list <valtype>)
                 | (tuple <valtype>*)
                 | (flags <name>*)