Add description of label_html option

Author: przemyslaw-bogusz

reference/forms/types/button.rst

@@ -13,6 +13,7 @@ A simple, non-responsive button.
 | options              | - `attr_translation_parameters`_                                     |
 |                      | - `disabled`_                                                        |
 |                      | - `label`_                                                           |
+|                      | - `label_html`_                                                      |
 |                      | - `label_translation_parameters`_                                    |
 |                      | - `row_attr`_                                                        |
 |                      | - `translation_domain`_                                              |
@@ -53,6 +54,8 @@ as a key. This can be useful when you need to set a custom class for the button:
 
 .. include:: /reference/forms/types/options/button_label.rst.inc
 
+.. include:: /reference/forms/types/options/label_html.rst.inc
+
 .. include:: /reference/forms/types/options/button_translation_domain.rst.inc
 
 label_translation_parameters

reference/forms/types/form.rst

@@ -42,6 +42,7 @@ on all types for which ``FormType`` is the parent.
 |           | - `block_prefix`_                                                  |
 |           | - `disabled`_                                                      |
 |           | - `label`_                                                         |
+|           | - `label_html`_                                                    |
 |           | - `row_attr`_                                                      |
 |           | - `translation_domain`_                                            |
 |           | - `label_translation_parameters`_                                  |
@@ -172,6 +173,8 @@ of the form type tree (i.e. it cannot be used as a form type on its own).
 
 .. include:: /reference/forms/types/options/label.rst.inc
 
+.. include:: /reference/forms/types/options/label_html.rst.inc
+
 .. include:: /reference/forms/types/options/row_attr.rst.inc
 
 .. include:: /reference/forms/types/options/translation_domain.rst.inc

reference/forms/types/options/label_html.rst.inc

@@ -0,0 +1,8 @@
+label_html
+~~~~~~~~~
+
+**type**: ``bool`` **default**: ``false``
+
+By default, the contents of the ``label`` option are escaped before rendering
+them in the template. Set this option to ``true`` to not escape them, which is
+useful when the label contains HTML elements.