index of the loop that the block was retrieved with.

   Usage:

       Call this macro when the block class inherits from AbstractFormBlock to
       to render it correctly.

        {% import 'form_block.html' as form_block with context %}

       {% for block in page.streamfield %}
           {{ form_block.render(block, 'streamfield', loop.index0) }}
       {% endfor %}

   ========================================================================= #}

{%- macro render(block, fieldname, index) -%}
    {%- 