{{ header_tags }}

The header tags object is simply a shortcut placeholder for all of the tags that the system can determine should be output in the document header. This includes the page's "browser_title", "meta_description", "keywords", "meta_robots", and "canonical_url" values, as well as any scripts and stylesheets added to the head via the {% add_javascript %} and {% add_stylesheet %} tags.

Note that this object will only be evaluated once - if it is included twice in the document, the tags will still only be added once.