alternative for @U{} for older texinfo

[Assaf Gordon]

Hi,

In gnu sed we recently expanded the manual with unicode
content (e.g. '@U{FFFD}' commands in the texinfo file).

A user alerted us that this fails with older texinfo (5.2):
https://lists.gnu.org/archive/html/sed-devel/2017-06/msg00002.html

Checking the logs I see that @U{} was added circa 2014,
but it was only included in next official release (6.0)
in 2015.

Do you have any suggestions for an alternative that
would make it work (perhaps with degraded rendering)
on older texinfo ?
I would like to avoid requiring a new texinfo to build sed,
and but still like to include unicode characters in the manual.

Thanks!
- assaf