Checks if createContextualFragment is supported.
See also:
static bool get supportsCreateContextualFragment =>
    JS('bool', '("createContextualFragment" in window.Range.prototype)');
    © 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
    https://api.dart.dev/stable/2.5.0/dart-html/Range/supportsCreateContextualFragment.html