This is the the 3rd-party icalendar library, used for parsing and 
generating the text of ICS files.  It's included for source-code 
users who don't want to install it separately, and its license allows
this inclusion.

This library was patched locally in Oct-2025 for changes in Python.
Search .py files for "[3.0] fc" to find changes applied.

See its README and LICENSE for details of this package, or view at
https://pypi.org/project/icalendar/.