It is my variation of Fiona T/One Mad Tatter's variation of Anne Bruvold's TARDIS bookmark.
I made Fiona's version but wanted something a little longer so I added another row of rings to the filled in area.
This is the 3rd one I've made and with it I've decided that split chains aren't all that bad. A bit fiddly and I need to be in the right frame of mind to do them, but not as intimidating as I once thought. Shout out to everyone on YouTube you has made a video demo'ing this technique. I watched every one of them at least twice.