add comment about __array_prepare__ to 1.4 release notes

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/release/1.4.0-notes.rst b/doc/release/1.4.0-notes.rst
index e2df0322d..849b429cb 100644
--- a/doc/release/1.4.0-notes.rst
+++ b/doc/release/1.4.0-notes.rst
@@ -10,6 +10,19 @@ Highlights
 New features
 ============
 
+Extended array wrapping mechanism for ufuncs
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+An __array_prepare__ method has been added to ndarray to provide subclasses
+greater flexibility to interact with ufuncs and ufunc-like functions. ndarray
+already provided __array_wrap__, which allowed subclasses to set the array type
+for the result and populate metadata on the way out of the ufunc (as seen in
+the implementation of MaskedArray). For some applications it is necessary to
+provide checks and populate metadata *on the way in*. __array_prepare__ is
+therefore called just after the ufunc has initialized the output array but
+before computing the results and populating it. This way, checks can be made
+and errors raised before operations which may modify data in place.
+
 Automatic detection of forward incompatibilities
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~