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