Comment 2 for bug 1307553

Only bibs have source at the moment. Subfield $s seems fine for the purpose.

<dkyle> Drycona: guess I should ask in lp. was wondering what orgs might be using what 901 subfields already for their purposes.

Unless they've a local customization in place (which we can't officially care about), nobody is using subfields that aren't managed by the maintain_901() trigger function, as it completely replaces any existing 901 fields whenever a record gets updated.

For the record, here's the current 901 subfield list:

biblio
------
$a = TCN value
$b = TCN source
$c = bre.id
$t = 'biblio'
$o = owner
$d = share depth

authority
-----------
$c = are.id
$t = 'authority'

serial
------
$c = sre.id
$o = owning library
$r = serial.record_entry.record, i.e., the ID of the bib that the MFHD is linked to
$t = 'serial'