Document the changes in whats_new

jkseppan · jkseppan · commit eab297c8717e · 2017-01-05T19:29:50.000+02:00
diff --git a/doc/users/whats_new/reproducible_ps_pdf.rst b/doc/users/whats_new/reproducible_ps_pdf.rst
@@ -1,14 +1,26 @@
-Reproducible PS and PDF output
-------------------------------
+Reproducible PS, PDF and SVG output
+-----------------------------------
 
 The ``SOURCE_DATE_EPOCH`` environment variable can now be used to set
 the timestamp value in the PS and PDF outputs. See
 https://reproducible-builds.org/specs/source-date-epoch/
 
+Alternatively, calling ``savefig`` with ``metadata={creationDate=None}``
+will omit the timestamp altogether.
+
 The reproducibility of the output from the PS and PDF backends has so
 far been tested using various plot elements but only default values of
 options such as ``{ps,pdf}.fonttype`` that can affect the output at a
 low level, and not with the mathtext or usetex features. When
 matplotlib calls external tools (such as PS distillers or LaTeX) their
 versions need to be kept constant for reproducibility, and they may
 add sources of nondeterminism outside the control of matplotlib.
+
+For SVG output, the ``svg.hashsalt`` rc parameter has been added in an
+earlier release. In can be used to change some random id values in the
+output to be deterministic, at the cost that including multiple such
+svg files in one document can lead to collisions.
+
+These features are now enabled in the tests for the pdf and svg
+backends, so most test output files (but not all of them) are now
+deterministic.
