Only look for focusable PDOM elements if the target is actually under…

… the PDOM, see #1550

js/accessibility/FocusManager.ts

@@ -183,22 +183,19 @@ export default class FocusManager {
     assert && assert( document.activeElement, 'Must be called from focusin, therefore active elemetn expected' );
 
     if ( focus ) {
-      const uniqueId = document.activeElement!.getAttribute( PDOMUtils.DATA_PDOM_UNIQUE_ID )!;
-      assert && assert( uniqueId, 'Event target must have a unique ID on its data' );
-
-      // TODO: But maybe actually we have some clearing to do here. https://github.com/phetsims/scenery/issues/1550
-      // Cases like a DOM() HTML element don't have a uniqueID, should they?
-      if ( !uniqueId ) {
-        return;
-      }
 
       // Look for the scenery target under the PDOM
       for ( let i = 0; i < displays.length; i++ ) {
         const display = displays[ i ];
 
-        // null if target is not under the PDOM
-        const trail = PDOMInstance.uniqueIdToTrail( display, uniqueId );
-        if ( trail ) {
+        const activeElement = document.activeElement as HTMLElement;
+        if ( display.isElementUnderPDOM( activeElement ) ) {
+          const uniqueId = activeElement.getAttribute( PDOMUtils.DATA_PDOM_UNIQUE_ID )!;
+          assert && assert( uniqueId, 'Event target must have a unique ID on its data if it is in the PDOM.' );
+
+          const trail = PDOMInstance.uniqueIdToTrail( display, uniqueId )!;
+          assert && assert( trail, 'We must have a trail since the target was under the PDOM.' );
+
           const visualTrail = PDOMInstance.guessVisualTrail( trail, display.rootNode );
           if ( visualTrail.lastNode().focusable ) {
             FocusManager.pdomFocus = new Focus( display, visualTrail );

js/display/Display.ts

@@ -905,6 +905,13 @@ export default class Display {
     return this._accessible;
   }
 
+  /**
+   * Returns true if the element is in the PDOM. That is only possible if the display is accessible.
+   */
+  public isElementUnderPDOM( element: HTMLElement ): boolean {
+    return this._accessible && this.pdomRootElement!.contains( element );
+  }
+
   /**
    * Implements a workaround that prevents DOM focus from leaving the Display in FullScreen mode. There is
    * a bug in some browsers where DOM focus can be permanently lost if tabbing out of the FullScreen element,

js/input/Input.ts

@@ -1152,7 +1152,7 @@ export default class Input extends PhetioObject {
   public getRelatedTargetTrail( domEvent: FocusEvent | MouseEvent ): Trail | null {
     const relatedTargetElement = domEvent.relatedTarget;
 
-    if ( relatedTargetElement && this.isTargetUnderPDOM( relatedTargetElement as HTMLElement ) ) {
+    if ( relatedTargetElement && this.display.isElementUnderPDOM( relatedTargetElement as HTMLElement ) ) {
 
       const relatedTarget = ( domEvent.relatedTarget as unknown as Element );
       assert && assert( relatedTarget instanceof window.Element ); // eslint-disable-line no-simple-type-checking-assertions
@@ -1183,7 +1183,7 @@ export default class Input extends PhetioObject {
     else {
       const target = ( domEvent.target as unknown as Element );
       assert && assert( target instanceof window.Element ); // eslint-disable-line no-simple-type-checking-assertions
-      if ( target && this.isTargetUnderPDOM( target as HTMLElement ) ) {
+      if ( target && this.display.isElementUnderPDOM( target as HTMLElement ) ) {
         const trailIndices = target.getAttribute( PDOMUtils.DATA_PDOM_UNIQUE_ID );
         assert && assert( trailIndices, 'should not be null' );
         return PDOMInstance.uniqueIdToTrail( this.display, trailIndices! );
@@ -1636,7 +1636,7 @@ export default class Input extends PhetioObject {
     // if the event target is within the PDOM the AT is sending a fake pointer event to the document - do not
     // dispatch this since the PDOM should only handle Input.PDOM_EVENT_TYPES, and all other pointer input should
     // go through the Display div. Otherwise, activation will be duplicated when we handle pointer and PDOM events
-    if ( this.isTargetUnderPDOM( context.domEvent.target as HTMLElement ) ) {
+    if ( this.display.isElementUnderPDOM( context.domEvent.target as HTMLElement ) ) {
       return;
     }
 
@@ -1665,7 +1665,7 @@ export default class Input extends PhetioObject {
     // if the event target is within the PDOM the AT is sending a fake pointer event to the document - do not
     // dispatch this since the PDOM should only handle Input.PDOM_EVENT_TYPES, and all other pointer input should
     // go through the Display div. Otherwise, activation will be duplicated when we handle pointer and PDOM events
-    if ( this.isTargetUnderPDOM( context.domEvent.target as HTMLElement ) ) {
+    if ( this.display.isElementUnderPDOM( context.domEvent.target as HTMLElement ) ) {
       return;
     }
 
@@ -1943,13 +1943,6 @@ export default class Input extends PhetioObject {
     }
   }
 
-  /**
-   * Returns true if the Display is accessible and the element is a descendant of the Display PDOM.
-   */
-  private isTargetUnderPDOM( element: HTMLElement ): boolean {
-    return this.display._accessible && this.display.pdomRootElement!.contains( element );
-  }
-
   /**
    * Saves the main information we care about from a DOM `Event` into a JSON-like structure. To support
    * polymorphism, all supported DOM event keys that scenery uses will always be included in this serialization. If