Hi, sorry for the late reply. I will upload a Windows build in about 20 minutes, if you want to try it yourself 
You can check this other thread on devtalk for further discussion on this topic.
Anyway, regarding your question, if you use Y for twist, then Z and X components will be used for swinging the bone. Starting from rest pose, depending on the roll angle, changing the Z component can result in a rotation about the Y global axis.
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