handle case when container is focusable

Author: yjbanov

lib/web_ui/lib/src/engine/semantics/semantics.dart

@@ -643,10 +643,27 @@ final class GenericRole extends PrimaryRoleManager {
 
   @override
   bool focusAsRouteDefault() {
+    final Focusable? focusable = this.focusable;
+
+    if (focusable != null) {
+      return focusable.focusAsRouteDefault();
+    }
+
     if (semanticsObject.hasChildren || !semanticsObject.hasLabel) {
+      // Unless the container is explicitly focusable (handled above), do not
+      // autofocus on the container itself. Instead, look for a child to focus
+      // on.
       return false;
     }
-    element.tabIndex = 0;
+
+    // Plain text nodes should not be focusable via keyboard or mouse. They are
+    // only focusable for the purposes of focusing the screen reader. To achieve
+    // that -1 is used.
+    //
+    // See also:
+    //
+    // https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/tabindex
+    element.tabIndex = -1;
     element.focus();
     return true;
   }