function @BPMN_JS_FUNCTION_NAME_TAG@() {
    // form variable element collection, type variable id
    var variable = document.getElementById( 'variable_id' );

    // checks, if variable exists and has non-empty value
    if ( !( variable && variable.value ) ) {
        // custom message about form variable requirement
        alert( 'custom_message' );

        // negative validation, no activity acceptance
        return false;
    }

    // positive validation, activity acceptance
    return true;
}