LM5117: LM5117 CC/CV Schematic in SNVA829

I read the SNVA829 "How to Design a Simple Constant Current/Constant Voltage Buck Converter" app note and I noticed the gate drivers have some extra circuitry that I would like to know more about.  Most importantly why does this cc/cv regulator need this extra circuitry?  We are following the app note and want to get it right. The upper MOSFET gate driver has a parallel combination of a diode and resistor in series with the gate.  I assume that the upper gate drive external circuitry is intended to forward bias the diode during turn on then steer the discharge current from the MOSFET through the resistor during turn off.  I assume the zero ohm resistor is a placeholder which is tuned to slow down the turn off, but why?  The lower MOSFET gate driver has an external PNP where the base-emitter is in parallel with another diode and resistor all of which is in series with the gate.  This looks like it is intended to help turn off the lower MOSFET, but why?  How do I select the correct resistor values and why am I doing it?