TYPO3 Core

I'm currently trying to make the new Form rendering produce html markup for Bootstrap.
One thing that doesn't properly work is currently the elementWrap.

For example, if you try to set the layout of the elementWrap like this:

tt_content.mailform.20.layout {
    elementWrap (
        <div class="control-group">
            <element />
        </div>
    )
}

It will always ignore/override that class attribute and produce this instead:

<div class="csc-form-* csc-form-element csc-form-element-*">...</div>

This is caused by the ContainerElementView in line 61:

$childNode->setAttribute('class', $child->getElementWraps());

This line should should append the class instead of overriding it:

$class = strlen($childNode->getAttribute('class')) > 0 ? $childNode->getAttribute('class') . ' ' : '';
$class .= $child->getElementWraps();
$childNode->setAttribute('class', $class);