FIX Field 223
The rate of interest that, when multiplied by the principal, par value, or face value of a bond, provides the currency amount of the periodic interest payment. The coupon is always cited, along with maturity, in any quotation of a bond's price.
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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.