From b2evolution manual

This tag inserts the RDF code necessary for automatic trackback discovery.

WARNING: this will serve spam bots more than anything else! If you add this to your blog you'll probably get 10 times more spam and normal users don't really need this.

[edit] Example

<source lang="php"> $Item->trackback_rdf(); </source>

[edit] Parameters

This tag does not accept any parameters.

[edit] Return value

This function return false, if trackbacks are not allowed on this blog.
If trackbacks are allowed then this function return true and displays content.