In the example in the sources, the coupon is the previous period's coupon plus an add-on minus the floating rate, and it is set to 0% if the result is negative. A bond whose coupon for a period depends on the floating rate and the previous period's coupon is called a snowball note.
Consider a hypothetical example in which the previous period's rate is 4.0%, the add-on is 2.0%, and the floating rate is 1.0%. The rate for the period is 4.0% + 2.0% − 1.0% = 5.0%. If the floating rate is 7.0%, the result is −1.0% and the rate is 0%.
Because the coupon depends on how rates have moved up to that period, it behaves differently from a floating-rate note, whose coupon depends only on that period's rate.