This operator will mirror the selected bones along the X axis based on Blender's bone naming convention for symmetrical armatures, either from left to right or right to left, depending on the selection.
If the side of the bone cannot be determined, it will be ignored.
Bones with the opposite names that don't yet exist will be created, and already existing ones will be overwritten. If matching bones are selected on both sides, mirroring will happen from right to left.
Symmetrized bone and constraint properties will have the necessary changes to mirror their behaviors. When symmetrizing bones with Action Constraints, the necessary keyframes will be added to the target Action to result in symmetrical movement when the Action is activated.
Note that bone or constraint drivers will not be created or affected in any way.