{% comment %}
A 'sequence' is a generalised structure that implements a collection
of blocks that can be ordered, added and deleted.
It provides the overall HTML structure, and the logic for updating
hidden fields to reflect changes to the sequence, but NOT the UI
controls for performing those changes: that is the responsibility of
specific subtypes of 'sequence', such as list and stream.
DO NOT PUT UI CONTROLS HERE, OR ANYTHING ELSE THAT ASSUMES A
SPECIFIC VISUAL RENDERING OF THE LIST.
(That belongs in templates that extend this one, such as list.html
and stream.html.)
{% endcomment %}
{% if help_text %}