The actual release names dropped the 5.x.x scheme long ago, so there is
no reason to keep it in the docs. It's extra confusing there because the
version is given as a two-part version (e.g. 5.1) most of the time, so
it looks like everything happened in OC 5.x, even though the change was
actually in OC x.0.
When using AttachMesh() with the flag AM_MatchSkeleton the behaviour was changed. The child mesh no longer uses the transformation of the bone in the parent skeleton by order, but by name.