I found this definition from
Eiusdemmodi which is referenced as the Documentation for CRT EmuDriver but the most recent information is from 2014 and the description of the last values on the site don't match any of the presets as all the presets have 4 values after VSyncPol rather then these two.
monitor_specs_{0-6} = "HfreqMin-HfreqMax, VfreqMin-VfreqMax, HFrontPorch, HSyncPulse, HBackPorch, VfrontPorch, VSyncPulse, VBackPorch, HSyncPol, VSyncPol,
ActiveLinesLimit, VirtualLinesLimit"
Example Preset:
monitor "arcade_31", "Arcade 31.5 kHz - high resolution", "4:3"
crt_range0 31400-31500, 49.50-65.00, 0.940, 3.770, 1.890, 0.349, 0.064, 1.017, 0, 0, 384, 480, 768, 960