[css-nav-1] Modify spatialNavigationSearch with more detail

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -534,10 +534,14 @@ the User Agent must run the steps described below:
 :   <dfn method for=Element lt="spatialNavigationSearch(options)">spatialNavigationSearch(<var>dir</var>, <var>options</var>)</dfn>
 ::
     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.
+    2. Let <var>container</var> be
+        * if the value of {{SpatialNavigationSearchOptions/container}} attribute of <var>options</var> is not null,
+            * itself, if it is <a>sptial navigation container</a>.
+            * its nearest <a>spatial navigation container</a> ancestor, otherwise.
+        * else the element's nearest <a>spatial navigation container</a> ancestor.
+    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. Return the result of <a>selecting the best candidate</a> among <var>areas</var> within <var>container</var> in <var>direction</var> from the element.
 
 Note: When neither a container nor a list of candidates is provided,