[Koha] ISBN display

[Rubén Fernández Asensio]

Hello all,
I understand that by MARC specifications the ISBN hyphens "may be system 
generated as display constants" and are not supposed to be carried in 
the MARC record:
http://www.loc.gov/marc/bibliographic/bd020.html

However all OPAC views show them without hyphens and I haven't found any 
system preference to switch them on. On the contrary, I found references 
to a patch to suppress them, at least in MARC view:
https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=2592

What's the appropriate way to switch on hyphen display in Normal and 
ISBD views, if possible at all? I'm using Koha 18.05.

Ruben