I am looking for the "Format" of the "M15" files. (If that was not clear.)

I know there is a post somewhere in the forums, but I can not remember where I saw the link. I keep coming back here, thinking it is somewhere in the topic, "M15 Format"... or files... or resources...

I would like to know the structure, and data-value locations, so that I may manipulate and/or construct an M15 from scratch, using a formulated construction code to create the required output for the file. (And/or merge M15's safely into one file.)