This is the second step of the processing chain: The rendering part gets the data array prepared by FormDataCompiler and creates a result array containing HTML, CSS and JavaScript. This is then post-processed by a controller to feed it to the PageRenderer or to create an ajax response.

The rendering is a tree: The controller intitializes this by setting one container as renderType entry point within the data array, then hands over the full data array to the NodeFactory which looks up a class responsible for this renderType, and calls render() on it. A container class creates only a fraction of the full result, and delegates details to another container. The second one does another detail and calls a third one. This continues to happen until a single field should be rendered, at which point an element class is called taking care of one element.

Render tree example

Each container creates some "outer" part of the result, calls some sub-container or element, merges the sub-result with its own content and returns the merged array up again. The data array is given to each sub class along the way, and containers can add further render relevant data to it before giving it "down". The data array can not be given "up" in a changed way again. Inheritance of a data array is always top-bottom. Only HTML, CSS or JavaScript created by a sub-class is returned by the sub-class "up" again in a "result" array of a specified format.

class SomeContainer extends AbstractContainer
    public function render()
        $result = $this->initializeResultArray();
        $data = $this->data;
        $data['renderType'] = 'subContainer';
        $childArray = $this->nodeFactory->create($data)->render();
        $resultArray = $this->mergeChildReturnIntoExistingResult($result, $childArray, false);
        $result['html'] = '<h1>A headline</h1>' . $childArray['html'];
        return $result;

Above example lets NodeFactory find and compile some data from "subContainer", and merges the child result with its own. The helper methods initializeResultArray() and mergeChildReturnIntoExistingResult() help with combining CSS and JavaScript.

An upper container does not directly create an instance of a sub node (element or container) and never calls it directly. Instead, a node that wants to call a sub node only refers to it by a name, sets this name into the data array as $data['renderType'] and then gives the data array to the NodeFactory which determines an appropriate class name, instantiates and initializes the class, gives it the data array, and calls render() on it.


The SingleFieldContainer and FlexFormElementContainer will probably vanish with core version 9.


Data set by containers and given down to children will likely change in core version 9: All fields not registered in the main data array of FormDataCompiler and only added within containers will move into section renderData. Furthermore, it is planned to remove parameterArray and substitute it with something better. This will affect most elements and will probably break a lot of these elements.

Class inheritance

Main render class inheritance

All classes must implement NodeInterface to be routed through the NodeFactory. The AbstractNode implements some basic helpers for nodes, the two classes AbstractContainer and AbstractFormElement implement helpers for containers and elements respectively.

The call concept is simple: A first container is called, which either calls a container below or a single element. A single element never calls a container again.


The NodeFactory plays an important abstraction role within the render chain: Creation of child nodes is always routed through it, and the NodeFactory takes care of finding and validating the according class that should be called for a specific renderType. This is supported by an API that allows registering new renderTypes and overriding existing renderTypes with own implementations. This is true for all classes, including containers, elements, fieldInformation, fieldWizards and fieldControls. This means the child routing can be fully adapted and extended if needed. It is possible to transparently "kick-out" a core container and to substitute it with an own implementation.

As example, the TemplaVoila implementation needs to add additional render capabilities of the flex form rendering to add for instance an own multi-language rendering of flex fields. It does that by overriding the default flex container with own implementation:

// Default registration of "flex" in NodeFactory:
// 'flex' => \TYPO3\CMS\Backend\Form\Container\FlexFormEntryContainer::class,

// Register language aware flex form handling in FormEngine
$GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['nodeRegistry'][1443361297] = [
    'nodeName' => 'flex',
    'priority' => 40,
    'class' => \TYPO3\CMS\Compatibility6\Form\Container\FlexFormEntryContainer::class,

This re-routes the renderType "flex" to an own class. If multiple registrations for a single renderType exist, the one with highest priority wins.


The NodeFactory uses $data['renderType']. This has been introduced with core version 7 in TCA, and a couple of TCA fields actively use this renderType. However, it is important to understand the renderType is only used within the FormEngine and type is still a must-have setting for columns fields in TCA. Additionally, type can not be overridden in columnsOverrides. Basically, type specifies how the DataHandler should put data into the database, while renderType specifies how a single field is rendered. This additionally means there can exist multiple different renderTypes for a single type, and it means it is possible to invent a new renderType to render a single field differently, but still let the DataHandler persist it the usual way.

Adding a new renderType in ext_localconf.php

// Add new field type to NodeFactory
$GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['nodeRegistry'][1487112284] = [
    'nodeName' => 'selectTagCloud',
    'priority' => '70',
    'class' => \MyVendor\CoolTagCloud\Form\Element\SelectTagCloudElement::class,

And use it in TCA for a specific field, keeping the full database functionality in DataHandler together with the data preparation of FormDataCompiler, but just routing the rendering of that field to the new element:

$GLOBALS['TCA']['myTable']['columns']['myField'] = [
    'label' => 'Cool Tag cloud',
    'config' => [
        'type' => 'select',
        'renderType' => 'selectTagCloud',
        'foreign_table' => 'tx_cooltagcloud_availableTags',

The above examples are a static list of nodes that can be changed by settings in ext_localconf.php. If that is not enough, the NodeFactory can be extended with a resolver that is called dynamically for specific renderTypes. This resolver gets the full current data array at runtime and can either return NULL saying "not my job", or return the name of a class that should handle this node.

An example of this are the core internal rich text editors. Both "ckeditor" and "rtehtmlarea" register a resolver class that are called for node name "text", and if the TCA config enables the editor, and if the user has enabled rich text editing in his user settings, then the resolvers return their own RichTextElement class names to render a given text field:

// Register FormEngine node type resolver hook to render RTE in FormEngine if enabled
$GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['nodeResolver'][1480314091] = [
    'nodeName' => 'text',
    'priority' => 50,
    'class' => \TYPO3\CMS\RteCKEditor\Form\Resolver\RichTextNodeResolver::class,

The trick is here that "ckeditor" registers his resolver with ah higher priority (50) than "rtehtmlarea" (40), so the "ckeditor" resolver is called first and wins if both extensions are loaded and if both return a valid class name.

Result array

The array returned by every node looks like:

    'html' => '',
    'additionalInlineLanguageLabelFiles' => [],
    'stylesheetFiles' => [],
    'requireJsModules' => [],

CSS and language labels (which can be used in JS) are added with their file names in format EXT:extName/path/to/file. JavaScript is added only via RequireJS modules, the registration allows an init method to be called if the module is loaded by the browser.


The result array actually contains a couple of more fields, but those will vanish with further FormEngine refactoring steps. If using them, be prepared to adapt extensions later.

Node expansion

The "node expansion" classes FieldControl, FieldInformation and FieldWizard are called by containers and elements and allow "enriching" containers and elements. Which enrichments are called can be configured via TCA.

This API is the substitution of the old "TCA wizards array" and has been introduced with core version 8.

Additional information. In elements, their output is shown between the field label and the element itself. They can not add functionality, but only simple and restricted HTML strings. No buttons, no images. An example usage could be an extension that auto-translates a field content and outputs an information like "Hey, this field was auto-filled for you by an automatic translation wizard. Maybe you want to check the content".
Wizards shown below the element. "enrich" an element with additional functionality. The localization wizard and the file upload wizard of type=group fields are examples of that.
"Buttons", usually shown next to the element. For type=group the "list" button and the "element browser" button are examples. A field control must return an icon identifier.

Currently, all elements usually implement all three of these, except in cases where it does not make sense. This API allows adding functionality to single nodes, without overriding the whole node. Containers and elements can come with default expansions (and usually do). TCA configuration can be used to add own stuff. On container side the implementation is still basic, only OuterWrapContainer and InlineControlContainer currently implement FieldInformation and FieldWizard.

See the TCA reference ctrl section for more information on how to configure these for containers in TCA.

Example. The InputTextElement (standard input element) defines a couple of default wizards and embeds them in its main result HTML:

class InputTextElement extends AbstractFormElement
    protected $defaultFieldWizard = [
        'localizationStateSelector' => [
            'renderType' => 'localizationStateSelector',
        'otherLanguageContent' => [
            'renderType' => 'otherLanguageContent',
            'after' => [
        'defaultLanguageDifferences' => [
            'renderType' => 'defaultLanguageDifferences',
            'after' => [

    public function render()
        $resultArray = $this->initializeResultArray();

        $fieldWizardResult = $this->renderFieldWizard();
        $fieldWizardHtml = $fieldWizardResult['html'];
        $resultArray = $this->mergeChildReturnIntoExistingResult($resultArray, $fieldWizardResult, false);

        $mainFieldHtml = [];
        $mainFieldHtml[] = '<div class="form-control-wrap">';
        $mainFieldHtml[] =  '<div class="form-wizards-wrap">';
        $mainFieldHtml[] =      '<div class="form-wizards-element">';
        // Main HTML of element done here ...
        $mainFieldHtml[] =      '</div>';
        $mainFieldHtml[] =      '<div class="form-wizards-items-bottom">';
        $mainFieldHtml[] =          $fieldWizardHtml;
        $mainFieldHtml[] =      '</div>';
        $mainFieldHtml[] =  '</div>';
        $mainFieldHtml[] = '</div>';

        $resultArray['html'] = implode(LF, $mainFieldHtml);
        return $resultArray;

This element defines three wizards to be called by default. The renderType concept is re-used, the values localizationStateSelector are registered within the NodeFactory and resolve to class names. They can be overridden and extended like all other nodes. The $defaultFieldWizards are merged with TCA settings by the helper method renderFieldWizards(), which uses the DependencyOrderingService again.

It is possible to:

  • Override existing expansion nodes with own ones from extensions, even using the resolver mechanics is possible.
  • It is possible to disable single wizards via TCA
  • It is possible to add own expansion nodes at any position relative to the other nodes by specifying "before" and "after" in TCA.