[Reference][Form Types] Add missing options for "form" type

reference/forms/types/form.rst

@@ -59,3 +59,8 @@ on all fields.
 
 .. include:: /reference/forms/types/options/invalid_message_parameters.rst.inc
 
+.. include:: /reference/forms/types/options/extra_fields_message.rst.inc
+
+.. include:: /reference/forms/types/options/post_max_size_message.rst.inc
+
+.. include:: /reference/forms/types/options/pattern.rst.inc

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

@@ -0,0 +1,9 @@
+extra_fields_message
+~~~~~~~~~~~~~~~~~~~~
+
+**type**: ``string`` **default**: ``This form should not contain extra fields.``
+
+This is the validation error message that's used if the submitted form data
+contains one or more fields that are not part of the form definition. The
+placeholder ``{{ extra_fields }}`` can be used to display a comma separated
+list of the submitted extra field names.

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

@@ -0,0 +1,16 @@
+pattern
+~~~~~~~
+
+**type**: ``string`` **default**: ``null``
+
+This option adds a ``pattern`` attribute to restrict the field input by a
+regular expression.
+
+.. caution:
+
+    This validation is client-side only.
+
+.. note:
+
+    When using validation constraints, this option is set automatically
+    for some constraints to match the server-side validation.

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

@@ -0,0 +1,12 @@
+post_max_size_message
+~~~~~~~~~~~~~~~~~~~~~
+
+**type**: ``string`` **default**: ``The uploaded file was too large. Please try to upload a smaller file.``
+
+This is the validation error message that's used if submitted POST form data
+exceeds php.ini's ``post_max_size``. The ``{{ max }}`` placeholder can be used
+to display the allowed size.
+
+.. note:
+
+    Validating the ``post_max_size`` only happens on the root form.