Non-formal. Shown here to give an idea of the basic requirements of the program. I see no point to formalize them into single statement requirements at this time.

1. The program shall support "most" web server configurations without any adaptions, i.e. it shall be written in a standard programming language that exist on most web servers. Project decision: PHP
2. Installation and configuration must be simple (must take less than 15 minutes). The configuration settings shall be stored in one single PHP class.
3. Integration of ics-blog to a web site must be possible to do with maximum 5 PHP class and or function calls from an external index file.
4. It shall be simple to edit and add entries to the blog. Project decision: Use iCalendar files for data storage. They can be created and edited with almost any calendar program.