'opaque' flag?

[Tim Kientzle]

Does anyone understand the semantics of the 'opaque' flag?

I'm trying to understand an issue with packages built
on union file systems.  It appears the 'opaque' flag
is set on some symlinks, which the package tools then
archive.  The archived flag is somehow interfering with
later installation of the package.

I've read McKusick's paper on unionfs which explains
the opaque flag for directories created on a unionfs,
but I have a bunch of questions:
   * Why is it appearing on symlinks?
   * How could the opaque flag interfere with package installs?
   * Should bsdtar ignore opaque flags?

Any input appreciated,

Tim Kientzle