@register.tag
def head_include(parser, token):
    nodelist = parser.parse(('endhead_include',))
    parser.delete_first_token()
    return HeadBlock(nodelist)

class HeadBlock(template.Node):
    def __init__(self, nodelist):
        self.nodelist = nodelist

    def render(self, context):
        output = self.nodelist.render(context)
        addcategory("header", "%s\n" % (output))
        return None