I'm in the beginning stages of designing a timeline software. One of the main features of this software is intended to be that the users are not restricted to just the Gregorian Calendar. In fact, they should be able to define their own calendar within the program.
As such: Is there any existing standard or file format or the like to define a calendar system? I'm purposefully not specifying any specific features the format should have: For now I just want to find out if any such format exists at all.
Thank you very much!