src/vs/editor/contrib/readOnlyMessage/browser/contribution.ts/ReadOnlyMessageController/_onDidAttemptReadOnlyEdit
class ReadOnlyMessageController:	private _onDidAttemptReadOnlyEdit(): void {
		const messageController = MessageController.get(this.editor);
		if (messageController && this.editor.hasModel()) {
			if (this.editor.isSimpleWidget) {
				messageController.showMessage(nls.localize('editor.simple.readonly', "Cannot edit in read-only input"), this.editor.getPosition());
			} else {
				messageController.showMessage(nls.localize('editor.readonly', "Cannot edit in read-only editor"), this.editor.getPosition());
			}
		}
	}