Change finding candidates into finding focusable areas

By moving the stepts that take the direction and starting point into
account from finding candidates to selecting the best one,
the "finding candidates" method can be made more generic.

This patches does that, and renames the relevant algorithm and API
accordingly.

This includes a convenience method to grab the nearest spatnav container
ancestor.

Closes WICG#31

index.bs

@@ -629,9 +629,8 @@ enum SpatialNavigationDirection {
     "inside"
 };
 
-dictionary FindSpatNavCandidatesOptions {
-    required SpatialNavigationDirection dir;
-    Node? container;
+dictionary FocusableAreasOptions {
+    boolean visibleOnly = true;
 };
 
 dictionary SelectSpatNavBestCandidateOptions {
@@ -640,20 +639,25 @@ dictionary SelectSpatNavBestCandidateOptions {
 };
 
 partial interface Element {
-    sequence<Node> findSpatNavCandidates(FindSpatNavCandidatesOptions arg);
+    Node getSpatnavContainer();
+    sequence<Node> focusableAreas(optional FocusableAreasOptions arg);
     Node? selectSpatNavBestCandidate(SelectSpatNavBestCandidateOptions arg);
     Node? sequentialNavSearch(SequentialNavigationDirection dir);
 };
 </pre>
 
-<div algorithm="findSpatNavCandidates steps">
-The {{Element/findSpatNavCandidates()}} method must follow these steps:
-1. Let <var>d</var> be the argument's {{FindSpatNavCandidatesOptions/dir}} attribute
-2. Let <var>c</var> be the argument's {{FindSpatNavCandidatesOptions/container}} attribute
-3. If <var>c</var> is <code>null</code>,
-    set <var>c</var> to the nearest ancestor of eventTarget that is a <a>spatnav container</a>.
-4. Let <var>candidates</var> be the result of <a>finding candidates</a> within <var>c</var> in direction <var>d</var> starting from the element
-5. Let <var>anchors</var> be a <a for=list>clone</a> of <var>candidates</var>,
+<div algorithm="getSpatnavContainer steps">
+The {{Element/getSpatnavContainer()}} method must follow these steps:
+1. Return the nearest ancestor of the element that is a <a>spatnav container</a>
+
+</div>
+
+<div algorithm="focusableAreas steps">
+The {{Element/focusableAreas()}} method must follow these steps:
+1. Let <var>v</var> be the argument's {{FocusableAreasOptions/visibleOnly}} attribute if present,
+	or <code>true</code> otherwise.
+4. Let <var>areas</var> be the result of <a>finding focusable areas</a> within the element with the visibleOnly argument set to <var>v</var>
+5. 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>.
 6. Return <var>anchors</var>
 
@@ -848,10 +852,8 @@ To run the <dfn>spatial navigation steps</dfn> in <var>direction</var>, do the f
     Note: We special case the situation where we're navigating from the state where nothing was focused,
     to start searching from the edges of the viewport.
 3. Let <var>container</var> be the nearest ancestor of <var>eventTarget</var> that is a <a>spatnav container</a>.
-4. <i>Loop</i>: Let <var>candidates</var> be the result of <a>finding candidates</a>
+4. <i>Loop</i>: Let <var>candidates</var> be the result of <a>finding focusable areas</a>
     within <var>container</var>
-    in <var>direction</var>
-    starting from <var>startingPoint</var>
 5. If <var>candidates</var> is <code>null</code>:
     * If <var>container</var> is a <a>scroll container</a> that <a>can be manually scrolled</a>:
             1. <a>Fire an event</a> named <a event>navbeforescroll</a> at <var>eventTarget</var> using {{NavigationEvent}}
@@ -893,10 +895,8 @@ To run the <dfn>spatial navigation steps</dfn> in <var>direction</var>, do the f
 
 <div algorithm="to run the navigate inside steps">
 To run the <dfn>navigate inside steps</dfn> on <var>eventTarget</var>, do the following:
-1. Let <var>candidates</var> be the result of <a>finding candidates</a>
+1. Let <var>candidates</var> be the result of <a>finding focusable areas</a>
     within <var>eventTarget</var>
-    starting from <var>eventTarget</var>
-    in direction <code>inside</code>
 2. If <var>candidates</var> is <code>null</code>,
     <a>Fire an event</a> named <a event>navnotarget</a> at <var>eventTarget</var> using {{NavigationEvent}}
     with its {{NavigationEvent/dir}} set to <code>inside</code> and {{NavigationEvent/relatedTarget}} set to <var>eventTarget</var>
@@ -941,7 +941,7 @@ as well as from the <a href="https://www.w3.org/TR/WICD/#focus-handling">old WIC
 Implementors who find better approaches or refinements to these approaches are strongly
 encouraged to provide feedback and help improve this specification
 in order to maximize interoperability.
-In particular, divergences in how User Agents <a>find candidates</a>
+In particular, divergences in how User Agents <a>find focusable areas</a>
 may cause some elements to be focusable in some User Agents but not in others,
 which would be bad for users.
 
@@ -956,18 +956,21 @@ The <dfn>boundary box</dfn> of an object is defined as follows:
 
 Issue(w3c/csswg-drafts#2324): CSS should have a term for “border box taking into account corner shaping properties like border-radius”.
 
-<div algorithm="to find candidates">
+<div algorithm="to find focusable areas">
 
-To <dfn lt="find candidates | finding candidates">find candidates</dfn> within a containing element <var>C</var>,
-in a direction <var>D</var>,
-starting from <var>starting point</var>,
+To <dfn lt="find focusable areas | finding focusable areas">find candidates</dfn> within a containing element <var>C</var>,
+with an optional <var>visibleOnly</var> argument that defaults to <code>true</code>,
 follow the following steps:
 
 1. Let <var>focusables</var> be the <a spec=infra for="/">set</a> of all the <a>focusable areas</a> that are descendants of <var>C</var>.
 2. The UA should <a spec=infra for=set>remove</a> from <var>focusables</var> elements whose <a element-attr spec=html><code>tabindex</code></a> attribute is set to a negative value.
 
     Note: This is a "SHOULD" in order to mirror the exclusion of elements with negative tabindex
     from the <a>sequential focus navigation order</a> as defined in [[HTML#the-tabindex-attribute]].
+3. If <var>visibleOnly</var> is <code>false</code>,
+    return <var>focusables</var>.
+
+    Note: <var>focusables</var> may be empty
 3. Let <var>visibles</var> be the subset of items in <var>focusables</var>
     whose <a>boundary box</a>
     is at least partly within <var>C</var>'s <a>scrollport</a>.
@@ -992,16 +995,9 @@ follow the following steps:
     that authors forget to do so.
 
     Issue(w3c/csswg-drafts#2325): Some CSS spec needs to define hit testing.
-5.
-    * If <var>D</var> is <code>inside</code>,
-        let <var>candidates</var> be the same as <var>visibles</var>
-    * Else, let <var>candidates</var> be the subset of the items in <var>visibles</var>
-        whose <a>boundary box</a>'s geometric center is within the closed half plane
-        whose boundary goes through the geometric center of the <var>starting point</var>
-        and is perpendicular to <var>D</var>.
-6. Return <var>candidates</var>.
+5. Return <var>visibles</var>.
 
-    Note: <var>candidates</var> may be empty
+    Note: <var>visibles</var> may be empty
 
 </div>
 
@@ -1015,6 +1011,11 @@ follow the following steps:
 
 1. If <var>candidates</var> is <a spec=infra for=set>empty</a>, return <code>null</code>
 2. If <var>candidates</var> contains a single item, return that item
+3. If <var>dir</var> is not <code>inside</code>,
+	set <var>candidates</var> be the subset of its items
+        whose <a>boundary box</a>'s geometric center is within the closed half plane
+        whose boundary goes through the geometric center of the <var>starting point</var>
+        and is perpendicular to <var>D</var>.
 3. For each <var>candidate</var> in <var>candidates</var>,
     find the points <var>P1</var> inside the <a>boundary box</a> of <var>starting point</var>
     and <var>P2</var> inside the <a>boundary box</a> of <var>candidate</var>