@jusc, for now you have only one layer to overlay.
I hope menion changes that and you could put as much layers on top of each other as you like or as your device can handle. 
You missunderstood me
What I mean is, with a map
without contour lines you can choose a contour line overlay (if there is any)
or any other overlay, but not both.
So, if you want contour lines
plus any other overlay, the only way in the moment is to take jurajs maps with the contour lines as base map.
So I wonder, why some people want a separate contour line overlay for the moment, as long there is only one overlay possible.
BTW: Overlays seem to use more accu power and CPU at least for me. Did anybody else notice it?