Install Astro Grep. Point the directory at the Marlin folder. For the search text, enter: FILAMENT_RUNOUT_SENSOR And press the Search button. You might also want to search for FIL_RUNOUT_PIN
These searches will show you the places in the code base that are sensitive to the filament running out.
These searches will show you the places in the code base that are sensitive to the filament running out.