Is there anything described / specified / standardized concerning the binary coded information mentioned in the suibject?
Of course, the explanations should be applicable to more than one printer (vendor / driver).
Concerning what’s organized for printing by LibreOffice itself (not by the driver): Are the respective settings all available via API objects?
Nothing formally standardized.
The methods exist exactly to handle printer driver-specific BLOBs, so indeed, not only can it not applicable to more than one printer (let alone vendor), but may even change between the same printer’s driver versions.
The actual layout of the BLOB is specified, as usual 
, in the code.
Note that, besides the driver-specific BLOB obtained using GetDriverData() call there, there are many other elements packed in the final wrapping BLOB.
Thanks @mikekaganski!
I’m afraid I won’t understand in what way a driver can “teach its own language” to a corresponding printjob creator inside any software to allow for a reasonable response.
Shouldn’t be such things standardized at least in the way some RFC describes communication between softeware subsystems? (Sorry for my fancy terminology.)
This reminds me of DOS times decades ago when I had to read a dozen pages in a manual to find what initialization string I needed to send to a printer before the substantial data.
The data is platform-specific.
On Windows, it uses DocumentPropertiesW to obtain the current data from printer driver, and will use that as a BLOB (not modifying or interpreting, just storing and restoring and sending back to printer driver).
On Linux, the BLOB is prepared in JobData::getStreamBuffer, as property-value pairs.
On macOS, only a stub (4 bytes) is written, no actual data.