Well the procedure I use is go to the line in your code that you want to start from (actually starts from previous line to one you choose) There are different ways to get to the line, scrolling and clicking the line, clicking in window and scrolling with arrows on keyboard or I think, also typing a line number into the line number DRO will work although I have never used that method.
Anyway once you are where you want to be in the code window press RFH button, it will scroll through the code then a message will ask you to press Cycle Start for prep move, Prep move box will appear and if you are happy you press OK. Machine will move to numbers in prep move box then another message asking to press Cycle Start again once its there, press that and off it should go. If you are going in circles by doing that then there are issues, if you attach your xml I will see if I can replicate it here.
Hood
BTW Mach is Art the creator who is retired (or as retired as he can bear to be
) Brian, Scott and Andrew and their time is pretty much taken up with things. Apple on the other hand is a company that probably has thousands of employees and also charges a lot more for their products
There are lots of videos as well as the documentation but Mach moves fast so even they will be outdated but should give useful insights to new users.