So apparently only the rel attribute is recognized in all browsers when it has to do with a stylesheet. I didn't know that...I rarely use rel though unless it has to do with a code snippet I snagged somewhere that already has the attribute in it.
As the link points out, the rel attribute should only be used with the link tag.
The rel attribute is intended to show the relationship between one document and another. For <link>, which indicates only that a relationship exists, rel is used to indicate the nature of the relationship. Currently, this is one of the only cases where the use of the rel attribute is meaningful to a browser.
For the link tag, I believe there is also very limited support for "alternate", used to indicate the link points to a mirrored document or a translated version, or a version intended for display on an alternate type of device.
Most of the common rel values are intended for use with spiders, to indicate how documents linked with <a> are related to one another. It is possible however, that browsers will increase support for additional rel values, such as "help" and "copyright" to give users a simple and common mechanism for obtaining additional information about web applications.
The best way to learn anything, is to question everything.
Is Opera the only browser that truly supports (and displays) relative links? If present, Opera will display all of the following:
Opera also assigns hot keys to these links. Do other user agents such as screen readers, etc. do this as well?
What added SEO edge can be gained by using them on a site, if any? Would they dilute PR?