If you take a look at the file docs/creating_external_custom_fields.pod, from the tarball, it should explain it.
It’s a way of using an external data source as the list you can select from for a custom field. The main example given is for listing the groups in RT as selectable values.
I’m using it for a tie into our Asset database (using DBI)
Steve AndersonFrom: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Kenneth Crocker
Sent: 21 June 2010 5:33 PM
Subject: [rt-users] Configuration question
I have 3.8.7 installed into production. I was looking at the Configuration->Tools-> System Configuration settings and noticed one I hadn’t read anything about “CustomFieldValuesSource”. What does this do or how is it used?
This email has been scanned by Netintelligence
BiP Solutions Limited is a company registered in Scotland with Company
Number SC086146 and VAT number 383030966 and having its registered
office at Medius, 60 Pacific Quay, Glasgow, G51 1DZ.
This e-mail (and any attachment) is intended only for the attention of
the addressee(s). Its unauthorised use, disclosure, storage or copying
is not permitted. If you are not the intended recipient, please destroy
all copies and inform the sender by return e-mail.
This e-mail (whether you are the sender or the recipient) may be
monitored, recorded and retained by BiP Solutions Ltd.
E-mail monitoring/ blocking software may be used, and e-mail content may
be read at any time.You have a responsibility to ensure laws are not
broken when composing or forwarding e-mails and their contents.