diff --git a/JS.md b/JS.md
index 91a8aecc..313ffea9 100644
--- a/JS.md
+++ b/JS.md
@@ -7,6 +7,14 @@ be loaded and run directly from an HTML `<script type='module'>` tag—and
 any other Web API that loads ES6 modules via URL—as part of 
 [ES6 Module integration](Modules.md#integration-with-es6-modules).)
 
+## Post-MVP JavaScript API
+
+Some JavaScript APIs were added post-MVP and can be
+[feature-tested](FeatureTest.md) together. These are grouped together,
+and each group is denoted with one of the following symbols:
+
+* ⚜
+
 ## Traps
 
 Whenever WebAssembly semantics specify a [trap](Semantics.md#traps),
@@ -510,11 +518,12 @@ call one with the `new` operator.
 
 A `WebAssembly.Memory` object contains a single [linear memory](Semantics.md#linear-memory)
 which can be simultaneously referenced by multiple `Instance` objects. Each
-`Memory` object has two internal slots:
+`Memory` object has three internal slots:
 
  * [[Memory]] : a [`Memory.memory`](https://github.com/WebAssembly/spec/blob/master/interpreter/spec/memory.mli)
  * [[BufferObject]] : the current `ArrayBuffer` whose [[ArrayBufferByteLength]]
    matches the current byte length of [[Memory]]
+ * [[Maximum]] : the `maximum` number of WebAssembly pages, or `undefined` if `maximum` is `None`
 
 ### `WebAssembly.Memory` Constructor
 
@@ -559,8 +568,10 @@ Any attempts to [`detach`](http://tc39.github.io/ecma262/#sec-detacharraybuffer)
 the detachment performed by [`m.grow`](#webassemblymemoryprototypegrow) shall throw a 
 [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
 
-Return a new `WebAssembly.Memory` instance with [[Memory]] set to `m` and
-[[BufferObject]] set to `buffer`.
+Return a new `WebAssembly.Memory` instance with
+[[Memory]] set to `m`,
+[[BufferObject]] set to `buffer`, and
+[[Maximum]] set to `undefined` if `maximum` is `None` or `maximum` otherwise.
 
 ### `WebAssembly.Memory.prototype [ @@toStringTag ]` Property
 
@@ -608,6 +619,30 @@ accessor function performs the following steps:
 If `this` is not a `WebAssembly.Memory`, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
 is thrown. Otherwise return `M.[[BufferObject]]`.
 
+### `WebAssembly.Memory.prototype.byteLength`
+
+[⚜](#Post-MVP-JavaScript-API)
+
+This is an accessor property whose [[Set]] is Undefined and whose [[Get]]
+accessor function performs the following steps:
+
+Let `T` be the `this` value. If `T` is not a `WebAssembly.Memory`, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
+is thrown.
+
+Return `T.[[BufferObject]].[[ArrayBufferByteLength]]`.
+
+### `WebAssembly.Memory.prototype.maximum`
+
+[⚜](#Post-MVP-JavaScript-API)
+
+This is an accessor property whose [[Set]] is Undefined and whose [[Get]]
+accessor function performs the following steps:
+
+Let `T` be the `this` value. If `T` is not a `WebAssembly.Memory`, a [`TypeError`](https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror)
+is thrown.
+
+Return `T.[[Maximum]]`.
+
 ## `WebAssembly.Table` Objects
 
 A `WebAssembly.Table` object contains a single [table](Semantics.md#table)