legend ignores artists with empty and _ labels

Author: xuanxu

tutorials/intermediate/legend_guide.py

@@ -44,7 +44,10 @@
 a list of handles/artists which exist on the Axes which can be used to
 generate entries for the resulting legend - it is worth noting however that
 not all artists can be added to a legend, at which point a "proxy" will have
-to be created (see :ref:`proxy_legend_handles` for further details).
+to be created (see :ref:`proxy_legend_handles` for further details). 
+
+Those artists with an empty string as label or with a label starting with
+"_" will be ignored.
 
 For full control of what is being added to the legend, it is common to pass
 the appropriate handles directly to :func:`legend`::