make @@toStringTag and constructor prototype properties funky accessors

spec.html

@@ -289,7 +289,35 @@ <h1>Iterator.prototype</h1>
 
       <emu-clause id="sec-iteratorprototype.constructor">
         <h1>Iterator.prototype.constructor</h1>
-        <p>The initial value of %Iterator.prototype%.constructor is %Iterator%.</p>
+        <p>`Iterator.prototype.constructor` is an accessor property with attributes { [[Enumerable]]: *false*, [[Configurable]]: *true* }. The [[Get]] and [[Set]] attributes are defined as follows:</p>
+
+        <emu-clause id="sec-get-iteratorprototype-constructor">
+          <h1>get Iterator.prototype.constructor</h1>
+          <p>The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:</p>
+          <emu-alg>
+            1. Return %Iterator%.
+          </emu-alg>
+        </emu-clause>
+
+        <emu-clause id="sec-set-iteratorprototype-constructor">
+          <h1>set Iterator.prototype.constructor</h1>
+          <p>The value of the [[Set]] attribute is a built-in function that takes an argument _v_. It performs the following steps when called:</p>
+          <emu-alg>
+            1. Let _O_ be ? RequireObjectCoercible(*this* value).
+            1. If _O_ is %Iterator.prototype%, then
+              1. Return *undefined*.
+            1. Let _desc_ be ? _O_.[[GetOwnProperty]](*"constructor"*).
+            1. If IsDataDescriptor(_desc_) is *true* and _desc_.[[Writable]] is *false*, then
+              1. Return *undefined*.
+            1. Let _newDesc_ be the PropertyDescriptor { [[Value]]: _v_, [[Writable]]: *true*, [[Enumerable]]: *false*, [[Configurable]]: *true* }.
+            1. Perform ? _O_.[[DefineOwnProperty]](*"constructor"*, _newDesc_).
+            1. Return *undefined*.
+          </emu-alg>
+        </emu-clause>
+
+        <emu-note>
+          <p>Unlike the *"constructor"* property on most built-in prototypes, for web-compatibility reasons this property must be an accessor.</p>
+        </emu-note>
       </emu-clause>
 
       <emu-clause id="sec-iteratorprototype.map">
@@ -563,9 +591,34 @@ <h1>Iterator.prototype.find ( _predicate_ )</h1>
 
       <emu-clause id="sec-iteratorprototype-@@tostringtag">
         <h1>Iterator.prototype [ @@toStringTag ]</h1>
-        <p>The initial value of the @@toStringTag property is the String value "Iterator".</p>
+        <p>`Iterator.prototype[@@toStringTag]` is an accessor property with attributes { [[Enumerable]]: *false*, [[Configurable]]: *true* }. The [[Get]] and [[Set]] attributes are defined as follows:</p>
+
+        <emu-clause id="sec-get-iteratorprototype-@@tostringtag">
+          <h1>get Iterator.prototype [ @@toStringTag ]</h1>
+          <p>The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:</p>
+          <emu-alg>
+            1. Return *"Iterator"*.
+          </emu-alg>
+        </emu-clause>
+
+        <emu-clause id="sec-set-iteratorprototype-@@tostringtag">
+          <h1>set Iterator.prototype [ @@toStringTag ]</h1>
+          <p>The value of the [[Set]] attribute is a built-in function that takes an argument _v_. It performs the following steps when called:</p>
+          <emu-alg>
+            1. Let _O_ be ? RequireObjectCoercible(*this* value).
+            1. If _O_ is %Iterator.prototype%, then
+              1. Return *undefined*.
+            1. Let _desc_ be ? _O_.[[GetOwnProperty]](@@toStringTag).
+            1. If IsDataDescriptor(_desc_) is *true* and _desc_.[[Writable]] is *false*, then
+              1. Return *undefined*.
+            1. Let _newDesc_ be the PropertyDescriptor { [[Value]]: _v_, [[Writable]]: *true*, [[Enumerable]]: *false*, [[Configurable]]: *true* }.
+            1. Perform ? _O_.[[DefineOwnProperty]](@@toStringTag, _newDesc_).
+            1. Return *undefined*.
+          </emu-alg>
+        </emu-clause>
+
         <emu-note>
-          <p>Unlike the @@toStringTag on most built-in classes, for web-compatibility reasons this property must be writable.</p>
+          <p>Unlike the @@toStringTag property on most built-in prototypes, for web-compatibility reasons this property must be an accessor.</p>
         </emu-note>
       </emu-clause>
     </emu-clause>