I've switched the PlaceholdersTest from using the internal Placeholders class to the official API.
While doing so I figured that we should not yet add this functionality at all.
But first we should discuss this through with mp and ConfigJSR.
The reason is that variable replacement is already added in ConfigJSR but does not yet contain all the cases Romain has on it's wishlist.
Plus we also need to ensure that we do not loose too much performance.
A few of the replacement rules are quite a bit 'meta'.
Before we implement those I really need the use cases first.