This is a quote from myself (from a forum nobody read 
). it could be an alternative of z-buffer (or maybe it could complement with that)
Please, read this message kindly.
I do not write well in English, but I’ve got an idea to solve the problem with the layers order.
This is hard to explain, but users like Ramón always make comments on it.
Moho has a problem when it comes to modifying the order in which layers are placed. For instance, you have created a character and you want that character to put his hand inside his pocket. The pocket layer would be behind the hand layer, which forces you to think in different ways to get the result you are looking for. Having different groups of layers makes problems like this very hard to solve.
Ramón has proposed creating a “Z buffer”, in which the order of the layers would be their Z depth. The render process won’t work according to the groups of layers, but to it’s position in Z.
I think Ramon’s idea is pretty good, but it forces you to work with a Z depth. Moho is a great 2d software and I think a good solution should consider its 2d nature.
Considering that, I suggest:
A second layer window.
According to this, you would create and order your characters and the rest of your work in any way you want using the current layer window. But if you want to change the order during the animation process, you would be able to use a second layer window.
This second window would be the same as the previous one, but it will allow you to break the layer groups, according to the order in which you want the objects to appear.
Back to our example, if you want the pocket layer to be in the place where the hand layer is, you could take the hand layer and move it on. This movement will be recorded in the timeline (which will have to consider a special item for it), so all the movements you create during the animation process will be recorded and susceptible to modifications.
Finally, if you want the pocket to be underneath the hand again, you should grab the pocket layer and put it back to its original place.
because ALL layers in one group are always over or under than the other layers in other group... Well, seems that each group has his own "space rules" and they can´t "intervene" each other... A Pity because, in my opinion, this limits enormously all the posibilities of the program, especially in very complex animations with a lot of layers, where we are obligated to organize them in groups... A check box, for example, in Depth Sort tab and Proyect Setting Dialogue, that let us to choose between an "Universal Depth Mode" or a "Groupal Depth Mode" It'd save our lifes, well in my case I don't exaggerate (belive me), because this is the main cause of my headaches! 
Well, I wondered if everybody think the same and if all of us would want a feature like this...
) I say you THANK YOU 
for all that GREAT work that you are doing and for keep Moho SO alive 
