es6 proxy guide draft

website/guide/es6features.html

@@ -1,23 +1,47 @@
 <h1 id="es6features">Ecmascript E6 features</h1>
 
 <p>This section describes the small set of features Duktape borrows from the
-<a href="https://people.mozilla.org/~jorendorff/es6-draft.html">current ES6 draft</a>.
-These features are not fully compliant; the intent is to minimize custom features
-and to align with the coming ES6 specification.</p>
+<a href="https://people.mozilla.org/~jorendorff/es6-draft.html">current ES6 draft</a>
+("Version: Rev 23, April 5, 2014 Draft").  These features are not fully compliant;
+the intent is to minimize custom features and to align with the coming ES6 specification.</p>
 
 <h2 id="es6-proto">Object.setPrototypeOf and Object.prototype.__proto__</h2>
 
 <p><a href="https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.setprototypeof">Object.setPrototypeOf</a>
 allows user to set the internal prototype of an object which is not supported in
 Ecmascript E5.  The Ecmascript E6 draft also provides
-<a href="https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.__proto__">Object.prototype.__proto__</a>
-which is an accessor property (setter/getter) which provides the same functionality
+<a href="https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.__proto__">Object.prototype.__proto__</a>,
+an accessor property (setter/getter) which provides the same functionality
 but is compatible with existing code base which has relied on a non-standard
 <code>__proto__</code> property for a while.  Duktape does not support the
 <a href="https://people.mozilla.org/~jorendorff/es6-draft.html#sec-__proto___-property-names-in-object-initializers">__proto__ property name in an object initializer</a>.</p>
 
-<p>These custom features can be disabled with feature options.</p>
+<p>These custom features can be disabled with the feature options
+<code>DUK_OPT_NO_OBJECT_ES6_SETPROTOTYPEOF</code> and
+<code>DUK_OPT_NO_OBJECT_ES6_PROTO_PROPERTY</code>.</p>
 
 <h2 id="es6-proxy">Proxy object (subset)</h2>
 
-<p>FIXME.</p>
+<p>The Ecmascript E6 <code>Proxy</code> object allows property virtualization
+and fine-grained access control for accessing an underlying plain object.
+Duktape implements a strict subset of the <code>Proxy</code> object from the
+ES6 draft (Rev 23).</p>
+
+<p>Limitations include:</p>
+<ul>
+<li>Limited to <code>get</code>, <code>set</code>, <code>deleteProperty</code>
+    handler methods; ES6 draft allows a lot more, e.g. to interact with
+    properties being called or constructed, enumeration, etc.  This causes
+    odd behavior if you enumerate a proxy object, call
+    <code>Object.defineProperty()</code> with the proxy object as an argument,
+    etc.</li>
+<li>Proxy revocation feature of ES6 draft is not supported.</li>
+<li>The target and handler objects given to <code>new Proxy()</code> cannot
+    be proxy objects themselves.  ES6 poses no such limitation, but Duktape
+    enforces it to simplify the internal implementation.</li>
+<li>As ES6 is still in a draft phase so the subset implemented by Duktape
+    may not be forwards compatible.</li>
+</ul>
+
+<p>This custom feature can be disabled with the feature option
+<code>DUK_OPT_NO_ES6_PROXY</code>.</p>