Demonstrates an issue in semantic node focusability

focusable_platform_view.dart

import 'dart:ui_web' as ui_web;

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:web/web.dart' as web;

void main() async {
  _registerFactory();
  runApp(const MyApp());
  if (kIsWeb) {
    SemanticsBinding.instance.ensureSemantics();
  }
  await Future<void>.delayed(const Duration(seconds: 2));
  debugDumpSemanticsTree();
}

void _registerFactory() {
  ui_web.platformViewRegistry.registerViewFactory('dom_button', (int viewId) {
    final web.HTMLElement htmlElement =
      web.document.createElement('button') as web.HTMLDivElement;
    htmlElement.innerText = 'Button 2';
    htmlElement.style
      ..setProperty('width', '100%')
      ..setProperty('height', '100%');
    return htmlElement;
  });
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Focusable platform view',
      home: Scaffold(
        body: SizedBox(
          height: 100.0,
          child: HtmlElementView(viewType: 'dom_button'),
        ),
      ),
    );
  }
}

The semantics tree for this UI:

SemanticsNode#0
 │ Rect.fromLTRB(0.0, 0.0, 3456.0, 1988.0)
 │
 └─SemanticsNode#1
   │ Rect.fromLTRB(0.0, 0.0, 1728.0, 994.0) scaled by 2.0x
   │ textDirection: ltr
   │
   └─SemanticsNode#2
     │ Rect.fromLTRB(0.0, 0.0, 1728.0, 994.0)
     │ sortKey: OrdinalSortKey#3af28(order: 0.0)
     │
     └─SemanticsNode#3
       │ Rect.fromLTRB(0.0, 0.0, 1728.0, 994.0)
       │ flags: scopesRoute
       │
       └─SemanticsNode#4
         │ Rect.fromLTRB(0.0, 0.0, 1728.0, 100.0)
         │ flags: isFocusable
         │
         └─SemanticsNode#5
             Rect.fromLTRB(0.0, 0.0, 1728.0, 100.0)
             platformViewId: 0