findComposingRegion static method
Returns the current composing region for the SuperEditor matched by
finder, or the singular SuperEditor in the widget tree, if finder
is null.
By default, this method expects a single SuperEditor in the widget tree and
finds it byType. To specify one SuperEditor among many, pass a superEditorFinder.
Implementation
static DocumentRange? findComposingRegion([Finder? finder]) {
  final element = (finder ?? find.byType(SuperEditor)).evaluate().single as StatefulElement;
  final superEditor = element.state as SuperEditorState;
  return superEditor.editContext.composer.composingRegion.value;
}