Support overriding form classname and template within StructBlock

docs/topics/streamfield.rst

@@ -269,6 +269,24 @@ This defines ``PersonBlock()`` as a block type that can be re-used as many times
     ])
 
 
+To customise the styling of the block as it appears in the page editor, your subclass can specify a ``form_classname`` attribute in ``Meta`` to override the default value of ``struct-block``:
+
+.. code-block:: python
+
+    class PersonBlock(blocks.StructBlock):
+        first_name = blocks.CharBlock(required=True)
+        surname = blocks.CharBlock(required=True)
+        photo = ImageChooserBlock()
+        biography = blocks.RichTextBlock()
+
+        class Meta:
+            icon = 'user'
+            form_classname = 'person-block struct-block'
+
+
+You can then provide custom CSS for this block, targeted at the specified classname, by using the ``insert_editor_css`` hook (see :doc:`Hooks </reference/hooks>`). For more extensive customisations that require changes to the HTML markup as well, you can override the ``form_template`` attribute in ``Meta``.
+
+
 ListBlock
 ~~~~~~~~~
 

wagtail/wagtailadmin/templates/wagtailadmin/block_forms/struct.html

@@ -1,9 +1,9 @@
-<div class="struct-block">
+<div class="{{ classname }}">
     {% if help_text %}
         <div class="object-help help">{{ help_text }}</div>
     {% endif %}
     <ul>
-        {% for child in bound_child_blocks %}
+        {% for child in children.values %}
             <li>
                 {% if child.block.label %}
                     <label{% if child.id_for_label %} for="{{ child.id_for_label }}"{% endif %}>{{ child.block.label }}</label>

wagtail/wagtailcore/blocks/struct_block.py

@@ -23,6 +23,8 @@ class BaseStructBlock(Block):
     class Meta:
         default = {}
         template = "wagtailadmin/blocks/struct.html"
+        form_classname = 'struct-block'
+        form_template = 'wagtailadmin/block_forms/struct.html'
 
     def __init__(self, local_blocks=None, **kwargs):
         self._constructor_kwargs = kwargs
@@ -72,15 +74,19 @@ class BaseStructBlock(Block):
         else:
             error_dict = {}
 
-        bound_child_blocks = [
-            block.bind(value.get(name, block.get_default()), prefix="%s-%s" % (prefix, name),
-                errors=error_dict.get(name))
+        bound_child_blocks = collections.OrderedDict([
+            (
+                name,
+                block.bind(value.get(name, block.get_default()),
+                    prefix="%s-%s" % (prefix, name), errors=error_dict.get(name))
+            )
             for name, block in self.child_blocks.items()
-        ]
+        ])
 
-        return render_to_string('wagtailadmin/block_forms/struct.html', {
-            'bound_child_blocks': bound_child_blocks,
+        return render_to_string(self.meta.form_template, {
+            'children': bound_child_blocks,
             'help_text': getattr(self.meta, 'help_text', None),
+            'classname': self.meta.form_classname,
         })
 
     def value_from_datadict(self, data, files, prefix):