@Bob9 It's very complicated. These properties would ideally be implemented in ical4j, because standard properties should be in ical4j and shouldn't require custom (extended) properties in ical4android. So, you could write a patch to get those properties into ical4j (current ical4j version: 3.x). Next problem: This would have to be backported to ical4j 2.x, because ical4j 3.x requires Java 8, which is only available at Android 7+, while DAVdroid is for Android 4.4+ and we don't want to raise the minimum API level to Android 7 yet. So, you could make sure that those properties are available in ical4j 2.x, too. (Alternatively, you could play around to get ical4j 3.x working on Android 4.4+ with parts of the Java 8 API on older Android versions – this would be an ideal solution because ical4j 3.x is the future, but it it will be cumbersome.) Then those properties would have to be implemented in the ical4android Event/Task classes. This should be quite easy. To allow DAVdroid to use those properties, they should also be handled by AndroidEvent/AndroidTask, so this should be implemented too. At the moment, I don't have time for all of this, but if you want to write patches, please don't hesitate