REF=NOFOLLOW & REL=NOFOLLOW

which one is right?

[ashii]

To tell search engine don't follow this link which syntax is right?

REF=NOFOLLOW
OR
REL=NOFOLLOW

I look at websites & both are being used.

[phranque]

the html specification for the anchor tag only supports a "rel=" attribute, not a "ref=" attribute:
[w3.org...]

regarding the use of "rel=nofollow", which was instituted by google and is now supported by the other major SE's, a word from the preeminent blogger on the subject:
[mattcutts.com...]