[Koha] RLIN

[Paul]

I can't find anything in the documentation about RLIN, nor can I find it in 
the sql schema, so am looking for some assistance, please.

First (enquiring mind) what does the abbreviation stand for?

Secondly, if I understand correctly, it is used for indexing authority 
entries, but how can it be searched?

Example: the default 730 for "serials/continuing resources" shows only a 
single input line "9 (RLIN)" - obviously, I can add $a to get a searchable 
"UNIF_TITLE", but there must be some reason for the default to hide this 
option.

Thanks - Paul