What does this "-" in jinja2 template engine do?

I am learning jinja2 because Google App Engine recommends it.

I found this example on Wikipedia: http://en.wikipedia.org/wiki/Jinja_%28template_engine%29

  {%- for item in item_list %}
    {{ item }}{% if not loop.last %},{% endif %}
  {%- endfor %}

What is the "-" in "{%- for"?

Also, where can I find jinja2 examples (better with Google App Engine)?

Thanks a lot!