I am a little bit confused when I want to use the layer functions. Once objects and layers are moved vertically in the Z-order "up-" and "downwards". But then I can move objects to "next" and "previous" layer. :-O Is next the lower or higher layer ?

For me it makes more sense to call this functions also "move to lower" or "higher layer".

I agree. Maybe "Move One Layer Up" and "Move One Layer Down" would be better.