Definition of the coordinate system

From the simulation, I found it is a right-hand z-up coordinate system. But I am not quite certain about what the x, y, z axis mean in the bone space, like the definition of the joint on humanoid.xml?

<joint name='abdomen_z' type='hinge' pos='0 0 0.065' axis='0 0 1' range='-45 45' damping='5' stiffness='20' armature='0.02' />

Is there any visualization on the axes definition? I am curious about this problem because I would like to calculate the inverse dynamics from motion captured data. It is very important to match the angles correctly.

 

I enabled the joint visualization with

Code:

option.flags[mjVIS_JOINT] = 1;
option.flags[mjVIS_TRANSPARENT] = 1;

But the coordinates are rendered all in blue.

 

the visualization on the coordinate