  We present the first high resolution photospheric X-ray spectrum of a
Supersoft X-ray Source, the famous CAL~83 in the Large Magellanic Cloud. The
spectrum was obtained with the Reflection Grating Spectrometer on XMM-Newton
during the Calibration/Performance Verification phase of the observatory. The
spectrum covers the range 20-40 A at an approximately constant resolution of
0.05 A, and shows very significant, intricate detail, that is very sensitive to
the physical properties of the object. We present the results of an initial
investigation of the spectrum, from which we draw the conclusion that the
spectral structure is probably dominated by numerous absorption features due to
transitions in the L-shells of the mid-$Z$ elements and the M-shell of Fe, in
addition to a few strong K-shell features due to CNO.
