what is the spec telling authors about missing link/@rel?

In 4.2.4 The link element:

"The types of link indicated (the relationships) are given by the value
of the rel attribute, which must be present, and must have a value that
is a set of space-separated tokens. The allowed values and their
meanings are defined in a later section. If the rel attribute is absent,
or if the values used are not allowed according to the definitions in
this specification, then the element does not define a link."

If the rel attribute is absent, than the "must be present" constraint
is violated and the document doesn't conform. Why tell authors
anything in that case?

Is this supposed to be marked as implementor advice?

Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E

Received on Thursday, 3 September 2009 17:57:59 UTC