The MEL I'd use to kind of figure out what is what...
Confirm it's a runTimeCommand...
whatIs AttachBrushToCurves
// Result: Run Time Command //
Query what command it calls when you call it...
runTimeCommand -q -command AttachBrushToCurves
// Result: convertCurvesToStrokes //
Figure out what that is...
whatIs convertCurvesToStrokes
// Result: Script found in: C:/Program Files/Autodesk/Maya2018/scripts/paintEffects/convertCurvesToStrokes.mel //
Then you can go open that .mel file to see what it does exactly. It does quite a bit, and I'm not sure what you want to do with it, so you might have to poke around there and see if you can pull out whatever it is you're looking for.
-Tim