I'd strongly advise any sane user to avoid looking at PPDs. Initially they were a fairly concise way for manufacturers to define the options a printer could support. They were written in a PostScript-ish format that wasn't impossible to follow. It used to be possible to build a new PPD from an old model printer's PPD and get a working, if limited, driver. 

CUPS changed all that. CUPS sticks far too much into a PPD: not just device specs, but proprietary driver features and almost all internationalized settings and error messages. This means that PPDs have lost much of their use as a config file and become effectively impenetrable. In trying to get an Epson printer to do everything that it's supposed to do, I had to hunt down the same setting in 11 different languages. If I left just one option off, the PPD failed with errors (sometimes in the language I hadn't fixed). It's all no fun. 

Cheers

 Stewart