Research: what is the iCalendar file format?

- What is the [**iCalendar**](https://en.wikipedia.org/wiki/ICalendar) format?
- What are the standard fields?
- Can we store additional information in an `.ics` file/record?

> Please write up your research findings to convey the information to a complete beginner.

Start with the linked iCalendar reference and investigate what the iCalendar format is, which standard fields it defines, and whether additional information can be stored in an .ics file or record. Done means publishing a beginner-friendly write-up that clearly answers all three questions.

Written by the indexing model from the issue text.