Alternative for PR 1957.

Fix for Issue #1619

webrtc.html

@@ -9674,10 +9674,6 @@ <h4><dfn>RTCDTMFSender</dfn></h4>
             <p>Let <var>dtmf</var> be a newly created
             <code><a>RTCDTMFSender</a></code> object.</p>
           </li>
-          <li>
-            <p>Let <var>dtmf</var> have a <dfn>[[\CanInsertDtmf]]</dfn>
-            internal slot, initialized to <code>false</code>.</p>
-          </li>
           <li>
             <p>Let <var>dtmf</var> have a <dfn>[[\Duration]]</dfn>
             internal slot.</p>
@@ -9712,7 +9708,9 @@ <h2>Attributes</h2>
             <dt><dfn data-idl><code>canInsertDTMF</code></dfn> of type <span class=
             "idlAttrType"><a>boolean</a></span>, readonly</dt>
             <dd>
-              <p>Whether the <a>RTCDTMFSender</a> is capable of sending DTMF.</p>
+              <p>Whether the <a>RTCDTMFSender</a> <var>dtmfSender</var> is capable of sending
+              DTMF. On getting, the user agent MUST return the result of running
+              <a>determine if DTMF can be sent</a> for <var>dtmfSender</var>.</p>
             </dd>
             <dt><code>toneBuffer</code> of type <span class=
             "idlAttrType"><a>DOMString</a></span>, readonly</dt>
@@ -9773,8 +9771,8 @@ <h2>Methods</h2>
                 <a>throw</a> an <code>InvalidStateError</code>.</li>
                 <li>Let <var>dtmf</var> be the <code><a>RTCDTMFSender</a></code>
                 associated with <var>sender</var>.</li>
-                <li>If <var>dtmf</var>'s <a>[[\CanInsertDTMF]]</a> internal slot
-                is <code>false</code>, <a>throw</a> an <code>InvalidStateError</code>.</li>
+                <li>If <a>determine if DTMF can be sent</a> for <var>dtmf</var> returns
+                <code>false</code>, <a>throw</a> an <code>InvalidStateError</code>.</li>
                 <li>Let <var>tones</var> be the method's first argument.</li>
                 <li>If <var>tones</var> contains any <a>unrecognized</a>
                 characters, <a>throw</a> an <code>InvalidCharacterError</code>.
@@ -9849,6 +9847,34 @@ <h2>Methods</h2>
         </section>
       </div>
     </section>
+    <section>
+      <h3>canInsertDTMF algorithm</h3>
+      <p>To <dfn>determine if DTMF can be sent</dfn> for an <code><a>RTCDTMFSender</a></code>
+      instance <var>dtmfSender</var>, the user agent MUST queue a task that runs the following steps:</p>
+      <ol>
+        <li>Let <var>sender</var> be the <code><a>RTCRtpSender</a></code> associated with
+        <var>dtmfSender</var>.</li>
+        <li>Let <var>transceiver</var> be the <code><a>RTCRtpTransceiver</a></code>
+        associated with <var>sender</var>.</li>
+        <li>Let <var>connection</var> be the <code><a>RTCPeerConnection</a></code> associated with
+        <var>transceiver</var>.</li>
+        <li>If <var>connection</var>'s <code><a>RTCPeerConnectionState</a></code> is not <code>"connected"</code>
+       return <code>false</code> and abort these steps.</li>
+        <li>If <code><var>sender</var>.track</code> is <code>null</code> return <code>false</code>
+        and abort these steps.</li>
+        <li>If <code><var>sender</var>.track.kind</code> is not <code>"audio"</code> return
+        <code>false</code> and abort these steps.</li>
+        <li>If <var>transceiver</var>'s <a>[[\CurrentDirection]]</a> slot is not set return
+        <code>false</code> and abort these steps.</li>
+        <li>If <var>transceiver</var>'s <a>[[\CurrentDirection]]</a> is neither <code>"sendrecv"</code>
+        nor <code>"sendonly"</code> return <code>false</code> and abort these steps.</li>
+        <li>If there is no value of <var>j</var> ranging from 0 to the number of
+        codecs, for which <code><var>sender</var>.getParameters().codecs[<var>j</var>].mimetype</code>
+        has the value <code>"audio/telephone-event"</code>, return <code>false</code>
+        and abort these steps.</li>
+        <li>Return <code>true</code>.</li>
+      </ol>
+    </section>
     <section>
       <h3><dfn>RTCDTMFToneChangeEvent</dfn></h3>
       <p>The <code><a>tonechange</a></code> event uses the