diff --git a/wagtail/wagtailadmin/static/wagtailadmin/js/blocks/sequence.js b/wagtail/wagtailadmin/static/wagtailadmin/js/blocks/sequence.js
index ff6f2641e..a7c671b25 100644
--- a/wagtail/wagtailadmin/static/wagtailadmin/js/blocks/sequence.js
+++ b/wagtail/wagtailadmin/static/wagtailadmin/js/blocks/sequence.js
@@ -1,9 +1,16 @@
-/* Operations on a sequence of items, common to both ListBlock and StreamBlock.
+/*
+
+Operations on a sequence of items, common to both ListBlock and StreamBlock.
+
 These assume the presence of a container element named "{prefix}-container" for each list item, and
 certain hidden fields such as "{prefix}-deleted" as defined in sequence_member.html, but make no assumptions
 about layout or visible controls within the block. 
+
 For example, they don't assume the presence of a 'delete' button - it's up to the specific subclass
 (list.js / stream.js) to attach this to the SequenceMember.delete method.
+
+CODE FOR SETTING UP SPECIFIC UI WIDGETS, SUCH AS DELETE BUTTONS OR MENUS, DOES NOT BELONG HERE.
+
 */
 (function($) {
     window.SequenceMember = function(sequence, prefix) {
diff --git a/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence.html b/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence.html
index 06ed9738b..1e6e0bb98 100644
--- a/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence.html
+++ b/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence.html
@@ -1,4 +1,17 @@
-{# Common HTML structure shared by list and stream blocks #}
+{% 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 %}
 <div class="sequence">
     <input type="hidden" name="{{ prefix }}-count" id="{{ prefix }}-count" value="{{ list_members_html|length }}">
     
diff --git a/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence_member.html b/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence_member.html
index 6fa8944ac..1d9a44566 100644
--- a/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence_member.html
+++ b/wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence_member.html
@@ -1,3 +1,17 @@
+{% 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_member.html and stream_member.html.)
+
+
+{% endcomment %}
 <li id="{{ prefix }}-container" class="sequence-member blockname-{{ block_type_name }}">
     <input type="hidden" id="{{ prefix }}-deleted" name="{{ prefix }}-deleted" value="">
     <input type="hidden" id="{{ prefix }}-order" name="{{ prefix }}-order" value="{{ index }}">