It contains the normal option declarations you'd expect in a PPD, for the various options known to the database. Cupsomatic opens the PPD, extracts the encapsulated execution data found there, and combines it with the user-provided option values to this to compute the proper command to execute for filtering. CUPS completely supports normal PPD option types, which include boolean values and enumerated choices. PPDs do not support arbitrary user-inputted numerical arguments, so the cupsomatic doesn't currently do anything much with these. I might pre-select a range of legal values and treat floats and ints as enumerated types.
Someone make a suggestion.
These now map sensibly to the PageSize, MediaType, and InputSlot enumerated selections, plus the boolean Duplex argument, if present.