When I access Facebook on the web, one section of my profile page, titled "Friends.... see all friends", displays a selection of 9 of my friends, in 3 rows by 3 columns. I have more than 9 friends and the 9 friends that displayed changes from day to day.
The section is only displayed to me on my profile page, and available not publicly.
How does Facebook determine which 9 of my friends to show me on any given day?