---
title: "Deprecation: #109102 - FormEngine \"additionalHiddenFields\" key"
manual: "TYPO3 Core Changelog"
version: "main"
permalink: "https://docs.typo3.org/permalink/changelog:deprecation-109102-1740480000"
source: "Changelog/14.2/Deprecation-109102-FormEngineAdditionalHiddenFields.rst"
typo3-version: "14.2"
typo3-major: 14
type: "deprecation"
issue: 109102
forge: "https://forge.typo3.org/issues/109102"
tags: ["Backend", "PHP-API", "NotScanned", "ext:backend"]
rendered: "2026-09-20T18:31:11+00:00"
---

# Deprecation: #109102 - FormEngine "additionalHiddenFields" key {#deprecation-109102-1740480000}

See [forge#109102](https://forge.typo3.org/issues/109102)

## Description {#description}

The `additionalHiddenFields` result array key in FormEngine was a legacy
mechanism that stored hidden `<input>` HTML strings separately from the
main `html` key. This indirection is no longer needed. Elements can simply
add their hidden fields to the `html` key.

The following have been deprecated:

-   The `additionalHiddenFields` key in FormEngine result arrays
-   `FormResult::$hiddenFieldsHtml`
-   `FormResultCollection::getHiddenFieldsHtml()`

## Impact {#impact}

Third-party FormEngine elements that add entries to
`$resultArray['additionalHiddenFields']` will trigger a PHP
`E_USER_DEPRECATED` level error when their result is merged via
`AbstractNode::mergeChildReturnIntoExistingResult()`.

## Affected installations {#affected-installations}

Installations with custom FormEngine elements or containers that populate the
`additionalHiddenFields` result array key.

## Migration {#migration}

Move hidden field HTML from `additionalHiddenFields` into the `html` key.

Before:

```php
$resultArray = $this->initializeResultArray();
$resultArray['additionalHiddenFields'][] =
    '<input type="hidden" name="myField" value="myValue" />';
```

After:

```php
$resultArray = $this->initializeResultArray();
$resultArray['html'] .=
    '<input type="hidden" name="myField" value="myValue" />';
```