diff --git a/_pytest/assertion/rewrite.py b/_pytest/assertion/rewrite.py
index 772f3ac03..6cb5ee96c 100644
--- a/_pytest/assertion/rewrite.py
+++ b/_pytest/assertion/rewrite.py
@@ -327,6 +327,13 @@ def rewrite_asserts(mod):
 
 
 def _saferepr(obj):
+    """Get a safe repr of an object for assertion error messages
+
+    The assertion formatting (util.format_explanation()) requires
+    newlines to be escaped since they are a special character for it.
+    But py.io.saferepr allows newlines, so we need to escape them
+    here.
+    """
     repr = py.io.saferepr(obj)
     if py.builtin._istext(repr):
         t = py.builtin.text