Help Documentation for VCF tags?

[j4nd3r53n]

I am looking for information about how to create vcard files that can be imported into Contacts on my android phone (GT-S7272C). Some of it I can get from generic documentation of the VCF format, but it seems that android uses a lot of android specific tags, like:

• X-ANDROID-CUSTOM:vnd.android.cursor.item/relation;Aaaaaaaaaa;1;;;;;;;;;;;;;

This is from a test contact entry I made, obviously. The first part seems to be the same for all of them, and a qualified guess would be that the entries after the subtype (here: relation) are fields that are parsed depending on the subtype. But is there any documentation anywhere of the specific format?

Also, the entries seem to be duplicated in the file - is this expected? At first I thought it might be because I had sent the file in an email, but if I export and then copy them off with adb, it is the same. It still shows correctly in the Contacts app.