Document inability to use names from 3.12, 1.13
You can't use names from 3.12 Image Channel Order and
3.13 Image Channel Data Type since in the intstruction grammar,
they are only used as return values, but never named arguments
to instructions.
diff --git a/syntax.md b/syntax.md
index af35051..e16142e 100644
--- a/syntax.md
+++ b/syntax.md
@@ -193,4 +193,9 @@
OpEnqueueKernel.
* Similarly for the names in section 3.25 Memory Semantics.
* Similarly for the names in section 3.27 Scope.
-
+* Some enumerants cannot be used by name, because they only name values
+returned by an instruction:
+ * Enumerants from 3.12 Image Channel Order name possible values returned
+ by the `OpImageQueryOrder` instruction.
+ * Enumerants from 3.13 Image Channel Data Type name possible values
+ returned by the `OpImageQueryFormat` instruction.
