Support Frontend Editing by EXT:frontend_editing:
If you want to get Mask elements work with the new frontend editing, follow theese steps:
1. Add 'xmlns:feedit="http://typo3.org/ns/TYPO3/CMS/FrontendEditing/ViewHelpers"' as namespace to html tag
2. Wrap the whole Mask content below with < feedit:contentEditable table="tt_content" uid="{data.uid}">MASK ELEMENT< /feedit:contentEditable>
3. Beware of the spaces in the view helper -> '< feedit:' and '< /feedit:' -> this is for a vaild comment here, delete them! ;)