Updates Imperative Slot API spec.

dom.bs

@@ -2195,10 +2195,24 @@ steps:</p>
  <li><p>If the <i>open flag</i> is set and <var>shadow</var>'s <a for=ShadowRoot>mode</a> is
  <em>not</em> "<code>open</code>", then return null.</p></li>
 
- <li><p>If the shadow's <a for=ShadowRoot>slot assignment</a> is set to "<code>manual</code>",
- return the associated <a>slot</a> in shadow where the <var>slottable</var> is
- <a href="https://html.spec.whatwg.org/multipage/scripting.html#dom-slot-assign"><code>assigned</code></a>,
- otherwise return null.</p></li>
+ <li><p>If the shadow's <a for=ShadowRoot>slot assignment</a> is set to "<code>manual</code>", then:</p>
+  <ol>
+   <li><p>Let <var>manuallyAssignedNodes</var> be nodes that are
+   <a href="https://html.spec.whatwg.org/multipage/scripting.html#dom-slot-assign"><code>assigned</code></a>
+   to a <a>slot</a> in <var>shadow</var>'s <a for=tree>descendants</a>.</p></li>
+
+   <li><p>If <var>nodeSlotMap</var> doesn't exists, let <var>nodeSlotMap</var> be an empty <a for=/>map</a>.</p></li>
+
+   <li><p>For each <var>node</var> in <var>manuallyAssignedNodes</var>, set <var>nodeSlotMap[node]</var>
+   to <a>slot</a>.</p></li>
+
+   <li><p>Set <var>manuallyAssignedNodes</var> to empty list.</p></li>
+
+   <li><p>If <var>nodeSlotMap[slottable]</var> exists, then return <var>nodeSlotMap[slottable]</var>.</p></li>
+
+   <li><p>Return null.</p></li>
+  </ol>
+ </li>
 
  <li><p>Return the first <a>slot</a> in <a>tree order</a> in <var>shadow</var>'s
  <a for=tree>descendants</a> whose <a for=slot>name</a> is <var>slottable</var>'s
@@ -5716,9 +5730,9 @@ invoked, must return a new {{DocumentFragment}} <a>node</a> whose <a for=Node>no
 [Exposed=Window]
 interface ShadowRoot : DocumentFragment {
   readonly attribute ShadowRootMode mode;
+  readonly attribute SlotAssignmentMode slotAssignment;
   readonly attribute Element host;
   attribute EventHandler onslotchange;
-  readonly attribute SlotAssignmentMode slotAssignment;
 };
 
 enum ShadowRootMode { "open", "closed" };
@@ -5739,7 +5753,7 @@ It is initially set to false.</p>
      consequences for innerHTML. -->
 
 <p><a for=/>Shadow roots</a> have an associated <dfn for=ShadowRoot>slot assignment</dfn>
-("<code>manual</code>" or "<code>auto</code>"), whose default value is "<code>auto</code>"</p>
+("<code>manual</code>" or "<code>auto</code>"), whose default value is "<code>auto</code>".</p>
 
 <p>A <a for=/>shadow root</a>'s <a>get the parent</a> algorithm, given an <var>event</var>, returns
 null if <var>event</var>'s <a>composed flag</a> is unset and <a for=/>shadow root</a> is the