symfony - enable debug in twig by placing this into app/config/config_dev.yml

gistfile1.md

twig:
    debug: %kernel.debug%
services:
   twig.extension.text:
       class: Twig_Extensions_Extension_Text
       tags:
           - { name: twig.extension }
   twig.extension.debug:
       class: Twig_Extensions_Extension_Debug
       tags:
           - { name: twig.extension }

gistfile2.twig

{% debug name_of_variable %}