An SGML identifier used as the target for hypertext links or for naming particular elements in associated style sheets. Valid names to script with are any alphanumeric string that begins with a letter. Valid special characters include underbar "_".
The REL attribute gives the relationship(s) described by the hypertext link from the anchor to the target. The value is a comma-separated list of relationship values. Values and their semantics will be registered by the HTML registration authority. The default relationship if none other is given is void. The REL attribute is only used when the HREF= attribute is present.