Orientation (Rotation) Euler angles & Constraints

As mentioned in the previous article, all bones have an orientation (rotation). This orientation mainly affects how constraints behave, but can also have an effect on IK solvers.

How does rotation even work in 3D? (Euler gimbal)
The easiest/most comprehensible way of storing rotation is by having 3 axes, that affect each other in an order.
This GIF shows an order of X Y Z (Red-Green-Blue)

there are 2 big perks of this system, Gimbal lock and what I call axis locking

Gimbal lock & quaternions
Gimbal lock is a problem where you're unable to rotate over a certain range withou the