Add tests for the case of <iterator>.return, as used in the iteration protocol, being an object that's uncallable and compares equal to `undefined`.

1 files changed, 10 insertions, 0 deletions

diff --git a/INTERPRETING.md b/INTERPRETING.md
index 20181314f..7904eb710 100644
--- a/INTERPRETING.md
+++ b/INTERPRETING.md
@@ -64,6 +64,16 @@ properties of the global scope prior to test execution.
         6. Return Completion(status).
 
   - **`global`** - a reference to the global object on which `$262` was initially defined
+  - **`uncallableAndIsHTMLDDA`** - a function that returns an object *`obj`* for
+    which [Call](https://tc39.github.io/ecma262/#sec-call)(*`obj`*, *any value*, «»)
+    throws a `TypeError`.  (The value of [IsCallable]()(*`obj`*) is unspecified:
+    a callable *`obj`* that throws a `TypeError` or an uncallable *`obj`* works
+    equally well.)  In hosts supporting the
+    [IsHTMLDDA](https://tc39.github.io/ecma262/#sec-IsHTMLDDA-internal-slot)
+    internal slot, *`obj`* must also have such a slot.  (These highly specific
+    behaviors are entirely motivated by the very few tests that use this.  Read
+    them for an explanation.)  Tests that use this function should be marked as
+    using the `uncallableAndIsHTMLDDA` feature.
   - **`agent`** - an ordinary object with the following properties:
     - **`start`** - a function that takes a script source string and runs
       the script in a concurrent agent.  Will block until that agent is