In a <tpl:Tags> loop or in the tag.html file, returns the URL of a feed related to a tag.

Selects the feed type to use: either atom (Atom) or rss2 (RSS2). Default value is rss2.

<a type="application/atom+xml" href="{{tpl:TagFeedURL type="atom"}}/comments"
  title="{{tpl:lang This tag's comments Atom feed}}" class="feed">{{tpl:lang Comments feed}}</a>