DOC Normalization is aka spatial sign preprocessing
@@ -452,6 +452,8 @@ The normalizer instance can then be used on sample vectors as any transformer::
array([[-0.70..., 0.70..., 0. ...]])
+Note: L2 normalization is also known as spatial sign preprocessing.
+
.. topic:: Sparse input
:func:`normalize` and :class:`Normalizer` accept **both dense array-like
