Printing on objects - Gcode questions  

Printing on objects - Gcode questions

Dear community,

I like to print on objects/materials. I cannot go into detail as it is confidential right now.
I have some question about the new MBL system, and it seems as Prusa is using new commands that are not yet described in Marlin FW documentation.

G29 P9 X10 Y-4 W32 H4

I believe this has to do with nozzle before probing, but what exactly?

Then comes MBL...

G29 P1 ; invalidate mbl & probe print area
G29 P1 X0 Y0 W50 H20 C ; probe near purge place
G29 P3.2 ; interpolate mbl probes
G29 P3.13 ; extrapolate mbl outside probe area

How does the printer now where the actual part will be printed? It is very important for me, that probing only happens within the boundaries of the printed part.
What das P3.2 and P3.13 actually do, I only know P3.

I guess G28 Z would be suitable for me, but I would like to automate this Z-homing to the centerplace of the printed object. A 2x2 probe area with  G29 arount this centerplace would be more accurate, but also here I miss an option/gcode.

I appreciate your support with this topic