Removed permission to do `voidExpression is T` and `.. is! T`.

docs/language/informal/generalized-void.md

Index: docs/language/informal/generalized-void.md
diff --git a/docs/language/informal/generalized-void.md b/docs/language/informal/generalized-void.md
index ddbc526c0f321ae5c503d61ac0d80c44edfe9339..e18caa5b2494adcf347893b4f46cbcaaca66ab5c 100644
--- a/docs/language/informal/generalized-void.md
+++ b/docs/language/informal/generalized-void.md
@@ -270,7 +270,6 @@ following situations:
 *   In the initialization and increment expressions of a for-loop,
     `for (e1; e2; e3) {..}`, `e1` and `e3` may have type void.
 *   In a typeCast `e as T`, `e` may have type void.
-*   In a typeTest `e is T` or `e is! T`, `e` may have type void.
 *   In a parenthesized expression `(e)`, `e` may have type void.
 *   In a return statement `return e;`, when the return type of the innermost
     enclosing function is the type void, `e` may have type void.
@@ -312,6 +311,8 @@ bound as `Object`.
 
 ## Updates
 
+*   August 16h 2017: Removed exceptions allowing `e is T` and `e is! T`.
+
 *   August 9th 2017: Transferred to SDK repo, docs/language/informal.
 
 *   July 16th 2017: Reformatted as a gist.