How to customize a CollectionType () element?

This Symfony2 documentation § shows an amazing method for setting up a single field. I use it a lot, but there is one specific one Typefor which it is difficult for me to configure: CollectionType()Setting up the collection itself is quite simple, you can do something like this:

{% block _mynamespace_mybundle_mytype_mycollectionfield_row %}
{% if prototype is defined %}
    {% set attr = attr|merge({'data-prototype': form_widget(prototype) }) %}
{% endif %}
{% spaceless %}
    <ul {{ block('widget_container_attributes') }}>
        {% spaceless %}
            {{ form_errors(form) }}
            {% for child in form %}
            <li>
              {{form_widget(child)}}
            </li>
            {% endfor %}
        {% endspaceless %}
        {{ form_rest(form) }}
    </ul>
{% endspaceless %}
{% endblock %}

But how can you customize each item in the collection? And how can you customize data-prototypeusing Twig ( data-prototype- a special attribute used to add new elements using js)?

I tried to do something like this (for data-prototype):

{% block _mynamespace_mybundle_mytype_mycollectionfield_$$name$$_row %}
customization ok!
{% endblock %}

But I get errors because I don’t know how to avoid $

As for the elements, I tried a lot of things:

{% block _mynamespace_mybundle_mytype_mycollectionfield_item_subfield_row %}
customization ok!
{% endblock %}

{% block _mynamespace_mybundle_mytype_mycollectionfield_element_subfield_row %}
customization ok!
{% endblock %}

None of them work.