diff --git a/source b/source
index 7c905d3f93f..e3d5ae8b3f9 100644
--- a/source
+++ b/source
@@ -2917,8 +2917,8 @@ a.setAttribute('href', 'http://example.com/'); // change the content attribute d
      <li><dfn data-noexport="" data-x="idl-ArrayBufferView" data-x-href="https://heycam.github.io/webidl/#common-ArrayBufferView"><code>ArrayBufferView</code></dfn>
      <li><dfn data-noexport="" data-x="idl-boolean" data-x-href="https://heycam.github.io/webidl/#idl-boolean"><code>boolean</code></dfn>
      <li><dfn data-noexport="" data-x="idl-DOMString" data-x-href="https://heycam.github.io/webidl/#idl-DOMString"><code>DOMString</code></dfn>
-     <li><dfn data-noexport="" data-x="idl-USVString" data-x-href="https://heycam.github.io/webidl/#idl-USVString"><code>USVString</code></dfn>
      <li><dfn data-noexport="" data-x="idl-double" data-x-href="https://heycam.github.io/webidl/#idl-double"><code>double</code></dfn>
+     <li><dfn data-noexport="" data-x="IDL enumeration" data-x-href="https://heycam.github.io/webidl/#idl-enums">enumeration</dfn>
      <li><dfn data-noexport="" data-x="idl-Error" data-x-href="https://heycam.github.io/webidl/#idl-Error"><code>Error</code></dfn>
      <li><dfn data-noexport="" data-x="idl-Function" data-x-href="https://heycam.github.io/webidl/#common-Function"><code>Function</code></dfn>
      <li><dfn data-noexport="" data-x="idl-long" data-x-href="https://heycam.github.io/webidl/#idl-long"><code>long</code></dfn>
@@ -2927,7 +2927,7 @@ a.setAttribute('href', 'http://example.com/'); // change the content attribute d
      <li><dfn data-noexport="" data-x="idl-Uint8ClampedArray" data-x-href="https://heycam.github.io/webidl/#idl-Uint8ClampedArray"><code>Uint8ClampedArray</code></dfn>
      <li><dfn data-noexport="" data-x="idl-unrestricted-double" data-x-href="https://heycam.github.io/webidl/#idl-unrestricted-double"><code>unrestricted double</code></dfn>
      <li><dfn data-noexport="" data-x="idl-unsigned-long" data-x-href="https://heycam.github.io/webidl/#idl-unsigned-long"><code>unsigned long</code></dfn>
-     <li><dfn data-noexport="" data-x="IDL enumeration" data-x-href="https://heycam.github.io/webidl/#idl-enums">enumeration</dfn>
+     <li><dfn data-noexport="" data-x="idl-USVString" data-x-href="https://heycam.github.io/webidl/#idl-USVString"><code>USVString</code></dfn>
 
     </ul>
 
@@ -66330,8 +66330,9 @@ console.log(plasticButton2.getAttribute("is")); // will output "plastic-button"<
    data-x="concept-custom-element-definition-lifecycle-callbacks">lifecycle callbacks</dfn></dt>
    <dd>A map, whose three keys are the strings "<code data-x="">connectedCallback</code>",
    "<code data-x="">disconnectedCallback</code>", and "<code
-   data-x="">attributeChangedCallback</code>". The corresponding values are either a JavaScript
-   function object, or undefined. By default the value of each entry is undefined.</dd>
+   data-x="">attributeChangedCallback</code>". The corresponding values are either a Web IDL
+   <code data-x="idl-Function">Function</code> callback function type value, or null. By default the
+   value of each entry is null.</dd>
 
    <dt>A <dfn data-x="concept-custom-element-definition-construction-stack">construction
    stack</dfn></dt>
@@ -66534,8 +66535,6 @@ dictionary <dfn>ElementDefinitionOptions</dfn> {
    <li><p>Add <var>constructor</var> to this <code>CustomElementsRegistry</code>'s <span>set of
    being-defined constructors</span>.</p></li>
 
-   <li><p><span>Prepare to run script</span> with the <span>current settings object</span>.</p></li>
-
    <li>
     <p>Run the following substeps while catching any exceptions:</p>
 
@@ -66546,35 +66545,44 @@ dictionary <dfn>ElementDefinitionOptions</dfn> {
      <li><p>If <span data-x="js-Type">Type</span>(<var>prototype</var>) is not Object, then throw a
      <code>TypeError</code> exception.</p></li>
 
-     <li><p>Let <var>connectedCallback</var> be <span data-x="js-Get">Get</span>(<var>prototype</var>,
-     "connectedCallback"). Rethrow any exceptions.</p></li>
+     <li><p>Let <var>connectedCallback</var>, <var>disconnectedCallback</var>, and
+     <var>attributeChangedCallback</var> be null.</p>
 
-     <li><p>If <var>connectedCallback</var> is not undefined, and
-     <span>IsCallable</span>(<var>connectedCallback</var>) is false, then throw a
-     <code>TypeError</code> exception.</p></li>
+     <li><p>Let <var>connectedCallbackValue</var> be <span
+     data-x="js-Get">Get</span>(<var>prototype</var>, "connectedCallback"). Rethrow any
+     exceptions.</p></li>
 
-     <li><p>Let <var>disconnectedCallback</var> be <span
+     <li><p>If <var>connectedCallbackValue</var> is not undefined, then set
+     <var>connectedCallback</var> to the result of <span
+     data-x="concept-idl-convert">converting</span> <var>connectedCallbackValue</var> to the Web IDL
+     <code data-x="idl-Function">Function</code> callback type. Rethrow any exceptions.</p></li>
+
+     <li><p>Let <var>disconnectedCallbackValue</var> be <span
      data-x="js-Get">Get</span>(<var>prototype</var>, "disconnectedCallback"). Rethrow any
      exceptions.</p></li>
 
-     <li><p>If <var>disconnectedCallback</var> is not undefined, and
-     <span>IsCallable</span>(<var>disconnectedCallback</var>) is false, then throw a
-     <code>TypeError</code> exception.</p></li>
+     <li><p>If <var>disconnectedCallbackValue</var> is not undefined, then set
+     <var>disconnectedCallback</var> to the result of <span
+     data-x="concept-idl-convert">converting</span> <var>disconnectedCallbackValue</var> to the Web
+     IDL <code data-x="idl-Function">Function</code> callback type. Rethrow any exceptions.</p></li>
 
-     <li><p>Let <var>attributeChangedCallback</var> be <span
+     <li><p>Let <var>attributeChangedCallbackValue</var> be <span
      data-x="js-Get">Get</span>(<var>prototype</var>, "attributeChangedCallback"). Rethrow any
      exceptions.</p></li>
 
+     <li><p>If <var>attributeChangedCallbackValue</var> is not undefined, then set
+     <var>attributeChangedCallback</var> to the result of <span
+     data-x="concept-idl-convert">converting</span> <var>attributeChangedCallbackValue</var> to the
+     Web IDL <code data-x="idl-Function">Function</code> callback type. Rethrow any
+     exceptions.</p></li>
+
      <li><p>Let <var>observedAttributes</var> be an empty <code
      data-x="">sequence&lt;DOMString></code>.</p></li>
 
      <li>
-      <p>If <var>attributeChangedCallback</var> is not undefined, then:</p>
+      <p>If <var>attributeChangedCallback</var> is not null, then:</p>
 
       <ol>
-       <li><p>If <span>IsCallable</span>(<var>attributeChangedCallback</var>) is false, then throw
-       a <code>TypeError</code> exception.</p></li>
-
        <li><p>Let <var>observedAttributesIterable</var> be <span
        data-x="js-Get">Get</span>(<var>constructor</var>, "observedAttributes"). Rethrow any
        exceptions.</p></li>
@@ -66590,9 +66598,6 @@ dictionary <dfn>ElementDefinitionOptions</dfn> {
     exception or not:</p>
 
     <ol>
-     <li><p><span>Clean up after running script</span> with the <span>current settings
-     object</span>.</p></li>
-
      <li><p>Remove <var>name</var> from this <code>CustomElementsRegistry</code>'s <span>set of
      being-defined names</span>.</p></li>
 
@@ -66964,7 +66969,7 @@ customElements.define("x-foo", class extends HTMLElement {
    data-x="concept-custom-element-definition-lifecycle-callbacks">lifecycle callbacks</span> with
    key <var>callbackName</var>.</p></li>
 
-   <li><p>If <var>callback</var> is undefined, then abort these steps.</p></li>
+   <li><p>If <var>callback</var> is null, then abort these steps.</p></li>
 
    <li>
     <p>If <var>callbackName</var> is "<code data-x="">attributeChangedCallback</code>", then:</p>