DOC: explain clipbox a bit better

Author: jklymak

lib/matplotlib/artist.py

@@ -765,6 +765,11 @@ def set_clip_box(self, clipbox):
         Parameters
         ----------
         clipbox : `.Bbox`
+
+            Typically would be created from a `.TransformedBbox`. For
+            instance ``TransformedBbox(Bbox([[0, 0], [1, 1]]), ax.transAxes)``
+            is the default clipping for an artist added to an Axes.
+
         """
         self.clipbox = clipbox
         self.pchanged()