[Validator] Documented the divisibleBy option of the Count constraint

Author: javiereguiluz

reference/constraints/Count.rst

@@ -6,7 +6,9 @@ Countable) element count is *between* some minimum and maximum value.
 
 ==========  ===================================================================
 Applies to  :ref:`property or method <validation-property-target>`
-Options     - `exactMessage`_
+Options     - `divisibleBy`_
+            - `divisibleByMessage`_
+            - `exactMessage`_
             - `groups`_
             - `max`_
             - `maxMessage`_
@@ -101,6 +103,44 @@ you might add the following:
 Options
 -------
 
+divisibleBy
+~~~~~~~~~~~
+
+**type**: ``integer`` **default**: null
+
+.. versionadded:: 5.1
+
+    The ``divisibleBy`` option was introduced in Symfony 5.1.
+
+Validates that the number of elements of the given collection is divisible by
+a certain number.
+
+.. seealso::
+
+    If you need to validate that other types of data different from collections
+    are divisible by a certain number, use the
+    :doc:`DivisibleBy </reference/constraints/DivisibleBy>` constraint.
+
+divisibleByMessage
+~~~~~~~~~~~~~~~~~~
+
+**type**: ``string`` **default**: ``The number of elements in this collection should be a multiple of {{ compared_value }}.``
+
+.. versionadded:: 5.1
+
+    The ``divisibleByMessage`` option was introduced in Symfony 5.1.
+
+The message that will be shown if the number of elements of the given collection
+is not divisible by the number defined in the ``divisibleBy`` option.
+
+You can use the following parameters in this message:
+
+========================  ===================================================
+Parameter                 Description
+========================  ===================================================
+``{{ compared_value }}``  The number configured in the ``divisibleBy`` option
+========================  ===================================================
+
 exactMessage
 ~~~~~~~~~~~~
 

reference/constraints/DivisibleBy.rst

@@ -3,6 +3,12 @@ DivisibleBy
 
 Validates that a value is divisible by another value, defined in the options.
 
+.. seealso::
+
+    If you need to validate that the number of elements in a collection is
+    divisible by a certain number, use the :doc:`Count </reference/constraints/Count>`
+    constraint with the ``divisibleBy`` option.
+
 ==========  ===================================================================
 Applies to  :ref:`property or method <validation-property-target>`
 Options     - `groups`_