STIS provides additional Available-but-Unsupported
capabilities beyond those which will be routinely supported. Section 2.3
describes the distinction between supported and available-but-unsupported modes, and the policy with regard to the use of the latter. A mode is a combination of aperture, optical element (and central wavelength setting), and detector.
This appendix to the STIS Instrument Handbook
indicates which modes are supported and gives information about the additional Available-but-Unsupported modes of STIS. Since all of the imaging capabilities are supported, it contains information relevant to spectroscopic observations only. Numerous entrance slits or apertures are supported for a limited set of optical elements and available for others, or are used in available mode only. A small number of central wavelength settings have been removed from the set of supported settings due to difficulties with them (e.g., order overlap).