FIX Field 660
Used to identify the source of the Account (1) code. This is especially useful if the account is a new account that the Respondent may not have setup yet in their system.
Please post comments, clarifications, examples here. Click on the edit button on the right and away you go!
Don't forget to refer to the FPL Discussion Groups to back up anything you write. You will often find the authoritative statements on matters of FIX specification interpretation there. Links from FIXwiki pages to relevant discussions on the FPL site are very valuable.
For example if you were writing a clarification on how to specify the "quantity" of an order in FIX, you might add the following relevant link, http://www.fixprotocol.org/discuss/read/f5014573, to back up your points.