SHELXL is a program for the refinement of crystal structures from diffraction data, and is
primarily intended for single crystal X-ray data of organic, inorganic and organometallic
structures, though it can also be used for refinement of macromolecules against high
resolution data. It is valid for all space groups in conventional settings and otherwise. Polar
axis restraints and special position constraints are generated automatically. The program can
handle disorder, twinning, and absolute structure determination, and provides a large variety
of restraints and constraints for the control of difficult refinements. This user guide is based on
the SHELX-97 manual, but has been brought up to date. See also Sheldrick (2008).