HTML4 definition of the 'rel' attribute. Here are some additional values, each of which can be used or omitted in any combination (unless otherwise noted, and except where prohibited by law) and their meanings, symmetry, transitivity and inverse if any. Please see the XFN home page for more information about XFN.
friendship (pick at most one)
- contact
- Someone you know how to get in touch with. Often symmetric.
- acquaintance
- Someone who you have exchanged greetings and not much (if any) more — maybe a short conversation or two. Often symmetric.
- friend
- Someone you are a friend to. A compatriot, buddy, home(boy|girl) that you know. Often symmetric.
physical
- met
- Someone who you have actually met in person. Symmetric.
professional
- co-worker
- Someone a person works with, or works at the same organization as. Symmetric. Usually transitive.
- colleague
- Someone in the same field of study/activity. Symmetric. Often transitive.
geographical (pick at most one)
- co-resident
- Someone you share a street address with. Symmetric and transitive.
- neighbor
- Someone who lives nearby, perhaps only at an adjacent street address or doorway. Symmetric. Often transitive.
family (pick at most one)
- child
- A person's genetic offspring, or someone that a person has adopted and takes care of. Inverse is parent.
- parent
- Inverse of child.
- sibling
- Someone a person shares a parent with. Symmetric. Usually transitive.
- spouse
- Someone you are married to. Symmetric. Not transitive.
- kin
- A relative, someone you consider part of your extended family. Symmetric and typically transitive.
romantic
- muse
- Someone who brings you inspiration. No inverse.
- crush
- Someone you have a crush on. No inverse.
- date
- Someone you are dating. Symmetric. Not transitive.
- sweetheart
- Someone with whom you are intimate and at least somewhat committed, typically exclusively. Symmetric. Not transitive.
identity
- me
- A link to yourself at a different URL. Exclusive of all other XFN values. Required symmetric. There is an implicit "me" relation from the contents of a directory to the directory itself.