The best introduction about Facebook's "Hack" language I found: Part 1: http://www.sitepoint.com/hhvm-hack-part-1/ http://www.sitepoint.com/hhvm-hack-part-1/

The best introduction about Facebook's "Hack" language I found: Part 1: http://www.sitepoint.com/hhvm-hack-part-1/ http://www.sitepoint.com/hhvm-hack-part-1/ Part 2: http://www.sitepoint.com/look-hack-php-replacement-hhvm/ http://www.sitepoint.com/look-hack-php-replacement-hhvm/ Would be great if Facebook would publish more official information.