I've just tried adding "See Also" link for the PR 236815 discussing a FreeBSD-specific problem in the port devel/glib20 to relevant recent upstream discussion of same problem at https://gitlab.gnome.org/GNOME/glib/issues/1638
But the Bugzilla rejected it with error "is not a valid URL to a bug".
It would be nice also to be allowed to link relevant pull request directly:
*** Bug 238557 has been marked as a duplicate of this bug. ***
I see this is done. Thank you! Closing the PR.