TYPO3 Core

When you view a page in a workspace, you get that little red box in the upper right corner, which tells you, that you now see a preview of a workspace. While you can already customize the box (layout and text), you can not completely disable it. This does not hurt for regular pages, but it can really cause headaches,
- when you create an xml based output (you then need to make the box to be a xml comment)
- or you create a json object, because you need full TSFE for an ajax request (json does not really accept any comments, so this request will always fail when there is something after the '}]')

Solution: add a new config option to disable the preview info

TS example:

ajaxPage = PAGE
ajaxPage.typeNum = 57
ajaxPage.config {
disableAllHeaderCode = 1
disablePreviewInfo = 1
additionalHeaders = Content-type:text/x-json
no_cache = 1
xhtml_cleaning = 0
admPanel = 0
}

(issue imported from #M16133)