localinfo attribute in DocBook 5.0

Before DocBook 5.0, olink supported a form of link
using the targetdocent, linkmode, and localinfo
attributes.  In Bob Stayton's book, this form of
olink is noted as obsolescent.

In DocBook 5.0, targetdocent and linkmode are gone,
as expected, but localinfo remains.

Looking back at the discussions about olink in DocBook
5.0 in the mailing list archive, I find explanations
of why targetdocent and linkmode are gone, but I can't
find any explanation of why localinfo stayed in 5.0.

Can anyone shed any light on localinfo and what its
role, if any, is now?

Thanks,
Dick Hamilton