The Sherpa package was developed by the Chandra X-ray Center (:term:`CXC`) as a general purpose fitting and modeling tool, with specializations for handling X-ray Astronomy data. It is provided as part of the :term:`CIAO` analysis package, where the code is the same as that available from the Sherpa GitHub page, with the following modifications:
- the I/O backend uses the CIAO library :term:`Crates` rather than :term:`Astropy`;
- a set of customized IPython routines are provided as part of CIAO that automatically loads Sherpa and adjusts the appearance of IPython (mainly changes to the prompt);
- and the CIAO version of Sherpa includes the optional XSPEC model library (:py:mod:`sherpa.astro.xspec`).
The online documentation provided for Sherpa as part of CIAO, namely https://cxc.harvard.edu/sherpa/, can be used with the standalone version of Sherpa, but note that the focus of this documentation is the :doc:`session-based API <ui/index>` provided by the :py:mod:`sherpa.astro.ui` and :py:mod:`sherpa.ui` modules. These are wrappers around the Object-Oriented interface described in this document, and data management and utility routines.