How do I make 'X-Axis Mirror' available in Pose Mode? More often that not, while posing an armature, I want to mirror the pose across the X-axis, so that when I move "brow.L", "brow.R" also moves in the same way.

You can copy and paste a mirrored pose, or select both bones prior to performing a transform, but both of these options aren't particularly good workflow wise.

In edit mode, in the tools panel, under options you can enable "X-Axis Mirror" to copy all transforms across the X-axis in real time, but this option is not available in pose mode.

I'm not very experienced with python, but edit source reveals:

col.prop(ob.data, "use_mirror_x")


My understanding is that "use_mirror_x" refers to a boolean property, but I have no idea how to find where that boolean property is defined or if it would be possible to modify it to get the same result in pose mode.

Any advice on this is appreciated. Maybe there's a better way to achieve this?

Thanks.
If you want to mirror your animation form the left side to the other side during pose mode you just need to select the whole left side then copy the pose with Ctrl+C.

After that press Ctrl+i to go to your right side and finally press Shift+Ctrl+V to paste the the X flipped pose, that way you'll have a perfect mirror of both side