[MRG] DOC Adds _pairwise property to dev docs
@@ -1225,6 +1225,14 @@ Optional Arguments
In iterative algorithms, the number of iterations should be specified by
an integer called ``n_iter``.
+Pairwise Attributes
+^^^^^^^^^^^^^^^^^^^
+
+An estimator that accept ``X`` of shape ``(n_samples, n_samples)`` and defines
+a :term:`_pairwise` property equal to ``True`` allows for cross-validation of
+the dataset, e.g. when ``X`` is a precomputed kernel matrix. Specifically,
+the :term:`_pairwise` property is used by ``utils.metaestimators._safe_split``
+to slice rows and columns.
Rolling your own estimator
==========================
