Used inside component, not in slot (not supported by Etch therefore not supported by EE)
Used in default slot content within slots.name.empty condition (not supported by Etch therefore not supported by EE)
Used in loop or condition blocks (not supported by Etch therefore not supported by EE)
Used inside component, in slot in nested component (not currently supported by EE, EE will display this as read-only placeholder but it can cause issues with displaying correct block content for other passthrough blocks therefore it is not recommended - when the new Etch APIs we requested have been released this should be fully supported)