PPD files are a common way to to describe different options supported by a printer.
Some printer models have optional hardware features and accessories that can be present or not (e.g. finishers, additional paper trays, etc.). The PPD specification defines the keyword "InstallableOptions" for a PPD option group that contains such options (s. section 5.4 in version 4.3 of the PPD specification) [1].

KDE's print dialog on Linux currently shows the "Installable Options". Thus a user can override the system-wide settings for those options using the print dialog (e.g. specify that the printer has a duplexer installed while it actually has not). While allowing the user to set individual values for most print options (like resolution, colour mode, ...), I think it would be better not to display the "Installable options".

As the values set for the installable options describe the actual hardware setup, they need to be changed only if the actual printer hardware configuration changes (e.g. an additional paper tray, finisher or duplexer is installed). They are not specific to individual print jobs.

Because of this, they are most probably best handled in the system-wide configuration to avoid that users accidently set wrong values for those options which may lead to unpredictable behaviour on the target device.


The PPD specification says about "Installable Options" (in section 5.4):
"[...] The PPD specification provides a way to describe these 
accessories, to label
them as optional and initially not installed, and a way to install them 
later.
Thus an application can list the installable options in its user 
interface, but
can display them in some special way (for instance, grayed out) to 
indicate
that the basic configuration does not support them. [...]"


I asked on the CUPS mailing list how installable options should be handled in an application's print dialog [2].
Michael Sweet (primary CUPS developer) replied there [3]:

"Generally speaking, we recommend that applications/toolkits *not* show installable options in the print dialog, and we provide API to determine whether a given option or choice is available (ppdInstallableConflict)."

The Gtk+ print dialog, for instance, also does not show these options.

[1] http://partners.adobe.com/public/developer/en/ps/5003.PPD_Spec_v4.3.pdf
[2] http://www.cups.org/pipermail/cups/2015-September/027112.html
[3] http://www.cups.org/pipermail/cups/2015-September/027124.html

Reproducible: Always

Steps to Reproduce:
1. set up a (pseudo) printer "test-printer" with a PPD that contains "Installabe Options", e.g. using the following command (no real printer is needed):
sudo lpadmin -p test-printer -v ipp://printer1.example.org/ipp -E -P Ricoh-MP_C3503-pxlcolor-Ricoh.ppd
2. start a KDE application (e.g. Okular)
3. open print dialog using "File" -> "Print" or Ctrl+P
4. select the printer "test-printer"
5. go to "Properties" -> "Advanced"

Actual Results:  
The "Installable Options" (for the attached PPD: "Large Capacity Tray", "Option Tray", "Internal ShiftTray", "Internal Tray 2", "External Tray", "Finisher") are shown and their values can be changed.

Expected Results:  
The "Installable Options" are either not shown at all or cannot be changed (e.g. they are greyed out).