Change the description about low level APIs

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -451,7 +451,7 @@ enum FocusableAreaSearchMode {
     "all"
 };
 
-dictionary FocusableAreasOptions {
+dictionary FocusableAreasOption {
     FocusableAreaSearchMode mode;
 };
 
@@ -463,8 +463,8 @@ dictionary SpatialNavigationSearchOptions {
 
 partial interface Element {
     Node getSpatialNavigationContainer();
-    sequence<Node> focusableAreas(optional FocusableAreasOptions arg);
-    Node? spatialNavigationSearch(SpatialNavigationSearchOptions arg);
+    sequence<Node> focusableAreas(optional FocusableAreasOption option);
+    Node? spatialNavigationSearch(SpatialNavigationSearchOptions options);
 };
 </pre>
 
@@ -475,19 +475,20 @@ More directional keywords or a numerical angle could be added.
 Note: the {{focusableAreas()}} and {{getSpatialNavigationContainer()}} methods are <a>at-risk</a>.
 
 <div algorithm="getSpatialNavigationContainer steps">
-The {{Element/getSpatialNavigationContainer()}} method must follow these steps:
+:   <dfn method for=Element lt="getSpatialNavigationContainer()">{{Element/getSpatialNavigationContainer()}}</dfn>
+::  Follows these steps:
 1. Return the element if it is a <a>spatial navigation container</a>,
     or the nearest ancestor of the element that is a <a>spatial navigation container</a>,
     or the <a>document</a> if the nearest <a>spatial navigation container</a> is the viewport.
-
 </div>
 
 <div algorithm="focusableAreas steps">
-The {{Element/focusableAreas()}} method must follow these steps:
+:   <dfn method for=Element lt="focusableAreas(option)">focusableAreas(<var>option</var>)</dfn>
+::  Follows these steps:
 1. Let <var>visibleOnly</var> be <code>false</code>
-    if the argument's {{FocusableAreasOptions/mode}} attribute is present and equal to <code>'all'</code>,
+    if <var>option</var> is present and it's value is equal to <code>'all'</code>,
     or <code>true</code> otherwise.
-2. Let <var>areas</var> be the result of <a>finding focusable areas</a> within the element with the <var>visibleOnly</var> argument.
+2. Let <var>areas</var> be the result of <a>finding focusable areas</a> within the element with the <var>visibleOnly</var>.
 3. Let <var>anchors</var> be a <a for=list>clone</a> of <var>areas</var>,
     with every <a>focusable area</a> which is not itself a <a>Node</a> replaced with its <a>DOM anchor</a>.
 4. Return <var>anchors</var>
@@ -523,12 +524,13 @@ The {{Element/focusableAreas()}} method must follow these steps:
 </div>
 
 <div algorithm="spatialNavigationSearch steps">
-The {{Element/spatialNavigationSearch()}} method must follow these steps:
-1. Let <var>direction</var> be the argument's {{SpatialNavigationSearchOptions/dir}} attribute.
-2. If the argument's {{SpatialNavigationSearchOptions/candidates}} attribute is not <code>null</code>,
-    then let <var>areas</var> be that attribute.
+:   <dfn method for=Element lt="spatialNavigationSearch(options)">spatialNavigationSearch(<var>options</var>)</dfn>
+::  Follows these steps:
+1. Let <var>direction</var> be the value of {{SpatialNavigationSearchOptions/dir}} attribute from <var>options</var>.
+2. If the value of {{SpatialNavigationSearchOptions/candidates}} attribute from <var>options</var> is not <code>null</code>,
+    then let <var>areas</var> be the corresponding value.
 3. Else, let <var>container</var> be
-    * the argument's {{SpatialNavigationSearchOptions/container}} attribute, if it is not <code>null</code>,
+    * the value of {{SpatialNavigationSearchOptions/container}} attribute from <var>options</var>, if it is not <code>null</code>,
     * the element's nearest <a>spatial navigation container</a> ancestor, otherwise.
 4. 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.