Add a what's new entry

afvincent · afvincent · commit c060842c8352 · 2017-02-17T09:12:45.000+01:00
diff --git a/doc/users/whats_new/validation_of_linestyle_rcparams.rst b/doc/users/whats_new/validation_of_linestyle_rcparams.rst
@@ -0,0 +1,31 @@
+Validation of line style rcParams
+---------------------------------
+
+Stricter validation
+```````````````````
+The validation of rcParams that are related to line styles
+(``lines.linestyle``, ``boxplot.*.linestyle``, ``grid.linestyle`` and
+``contour.negative_linestyle``) now effectively checks that the values
+are valid line styles. Strings like ``dashed`` or ``--`` are accepted,
+as well as even-length sequences of on-off ink like ``[1, 1.65]``. In
+this latter case, the offset value is handled internally and should *not*
+be provided by the user.
+
+The validation is case-insensitive.
+
+Deprecation of the former validators for ``contour.negative_linestyle``
+```````````````````````````````````````````````````````````````````````
+The new validation scheme replaces the former one used for the
+``contour.negative_linestyle`` rcParams, that was limited to ``solid``
+and ``dashed`` line styles.
+
+The former public validation functions ``validate_negative_linestyle``
+and ``validate_negative_linestyle_legacy`` will be deprecated in 2.1 and
+may be removed in 2.3. There are no public functions to replace them.
+
+Examples of use
+```````````````
+::
+
+....grid.linestyle             : (1, 3)   # loosely dotted grid lines
+    contour.negative_linestyle : dashdot  # previously only solid or dashed
