Merge "Add a modulo core constraint"

doc/source/developing_guides/pluginguide.rst

@@ -251,6 +251,12 @@ the end user.
   Constrains a numerical value.  Applicable to INTEGER and NUMBER.
   Both ``min`` and ``max`` default to ``None``.
 
+*Modulo(step, offset, description)*:
+  Starting with the specified ``offset``, every multiple of ``step`` is a valid
+  value. Applicable to INTEGER and NUMBER.
+
+  Available from template version 2017-02-24.
+
 *CustomConstraint(name, description, environment)*:
   This constructor brings in a named constraint class from an
   environment.  If the given environment is ``None`` (its default)

doc/source/template_guide/hot_spec.rst

@@ -532,6 +532,24 @@ following range constraint would allow for all numeric values between 0 and
 
    range: { min: 0, max: 10 }
 
+modulo
+++++++
+The ``modulo`` constraint applies to parameters of type ``number``. The value
+is valid if it is a multiple of ``step``, starting with ``offset``.
+
+The syntax of the ``modulo`` constraint is
+
+.. code-block:: yaml
+
+   modulo: { step: <step>, offset: <offset> }
+
+Both ``step`` and ``offset`` must be specified.
+
+For example, the following modulo constraint would only allow for odd numbers
+
+.. code-block:: yaml
+
+   modulo: { step: 2, offset: 1 }
 
 allowed_values
 ++++++++++++++