[css-nav-1] More precise description when the focus target loses the focus

Search origin should be set again if the focus target loses the focus.

More detailed cases are
(1) the focus target removed from the page
(2) the focus target becomes invisible or disabled

Therefore, more description about above cases had been added.
(1) Remove

Reference:
* https://html.spec.whatwg.org/#data-model
* https://html.spec.whatwg.org/multipage/infrastructure.html#nodes-are-removed

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -25,13 +25,17 @@ spec: ui-events; urlPrefix: https://w3c.github.io/uievents/;
 spec: html; urlPrefix: https://html.spec.whatwg.org/multipage/;
     urlPrefix: interaction.html
         type: dfn;
+            text: actually disabled; url: #concept-element-disabled
+            text: being rendered
+            text: control group
+            text: currently focused area of a top-level browsing context
             text: DOM anchor
+            text: expressly inert
             text: focusable area
-            text: currently focused area of a top-level browsing context
             text: sequential focus navigation order
             text: sequential focus navigation starting point
             text: sequential navigation search algorithm
-            text: control group
+            text: removed; url: #nodes-are-removed
     urlPrefix: dom.html
         type: dfn;
             text: the body element; url: #the-body-element-2
@@ -1085,12 +1089,15 @@ run the following steps:
     then return it.
 3. Otherwise, return <var>searchOrigin</var>.
 
-If the focus changes not by the spatial navigation, the <var>searchOrigin</var> is set from the <var>old focus target</var> as following:
+If the focus status changes not by the spatial navigation, the <var>searchOrigin</var> is set from the <var>old focus target</var> as following:
 1. If <var>old focus target</var> becomes out of the viewport by scrolling,
     then let <var>searchOrigin</var> be the scroll container which triggers the scroll behavior.
-2. If <var>old focus target</var> is inert,
+2. If <var>old focus target</var> becomes
+    <a>actually disabled</a> or
+    <a>expressly inert</a> or
+    not <a>being rendered</a>,
     then let <var>searchOrigin</var> be the [=boundary box=] of <var>old focus target</var>.
-3. If the property of <var>old focus target</var> changes to <code>display: none</code> or <code>visibility: hidden</code>,
+3. If <var>old focus target</var> is <a>removed</a>,
     then let <var>searchOrigin</var> be the [=boundary box=] of <var>old focus target</var>.
 4. Otherwise,
     let <var>searchOrigin</var> be the viewport of <var>old focus target</var>'s Document.