[css-nav-1] Update the spatialNavigationSearch steps with inside attribute

* Add the step for using `inside` attribute of `option` argument
* Modify that the `candidates` are assigned after assigning the `container`.

Related: w3c#3743

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -535,19 +535,20 @@ the User Agent must run the steps described below:
 </div>
 
 <div algorithm="spatialNavigationSearch steps">
-:   <dfn method for=Element lt="spatialNavigationSearch(options)">spatialNavigationSearch(<var>options</var>)</dfn>
+:   <dfn method for=Element lt="spatialNavigationSearch(options)">spatialNavigationSearch(<var>dir</var>, <var>options</var>)</dfn>
 ::
-    1. Let <var>direction</var> be the value of {{SpatialNavigationSearchOptions/dir}} attribute of <var>options</var>.
-    2.
-        * If the value of {{SpatialNavigationSearchOptions/candidates}} attribute of <var>options</var> is not <code>null</code>,
-            then let <var>areas</var> be the that value
-        * else,
-            1.
-                * If the value of {{SpatialNavigationSearchOptions/container}} attribute of <var>options</var> is not <code>null</code>,
-                    let <var>container</var> be that value
-                * else, let <var>container</var> be the element's nearest <a>spatial navigation container</a> ancestor.
-            2. Let <var>areas</var> be the result of <a>finding focusable areas</a> within <var>container</var>.
-    3. Return the result of <a>selecting the best candidate</a> within <var>areas</var> in direction <var>direction</var> from the element.
+    1. Let <var>direction</var> be the value of <var>dir</var>.
+    2. Let <var>container</var> be the the value of {{SpatialNavigationSearchOptions/container}} attribute of <var>options</var>
+        if it is not <code>null</code>, the element's nearest <a>spatial navigation container</a> ancestor otherwise.
+    3. Let <var>areas</var> be the value of {{SpatialNavigationSearchOptions/candidates}} attribute of <var>options</var>
+        if it is not <code>null</code>, result of <a>finding focusable areas</a> within <var>container</var> otherwise.
+    4. Let <var>insideFirst</var> be the value of {{SpatialNavigationSearchOptions/inside}} attribute of <var>options</var>
+        if it is not <code>null</code>, <code>false</code> otherwise.
+    5. If <var>insideFirst</var> is <code>true</code>,
+        then let <var>bestCandidate</var> be the result of <a>selecting the best candidate</a> within element with <var>direction</var>.
+        * If <var>bestCandidate</var> is not <code>null</code>, return <var>bestCandidate</var>. 
+        * Else, fallback to the next step.
+    6. Return the result of <a>selecting the best candidate</a> within <var>areas</var> in <var>direction</var> from the element.
 
 Note: When neither a container nor a list of candidates is provided,
 this only searches through the visible focusable areas of the nearest