_getFormHandlerKey() {
        if (!this._hasFormHandlerFunction()) {
            AutoNumericHelper.throwError(`Unable to retrieve the form handler name`);
        }

        const formHandlerName = this.parentForm.dataset.anFormHandler;
        if (formHandlerName === '') {
            AutoNumericHelper.throwError(`The form handler name is invalid`);
        }

        return formHandlerName;
    }
Return the form handler key name from the parent form element, for the global form handler list.

@returns {string|*}
@private