Backport PR matplotlib#27397: SpanSelector widget: Improve doc for extents

Author: story645

lib/matplotlib/widgets.py

@@ -2915,7 +2915,12 @@ def _snap(values, snap_values):
 
     @property
     def extents(self):
-        """Return extents of the span selector."""
+        """
+        (float, float)
+            The values, in data coordinates, for the start and end points of the current
+            selection. If there is no selection then the start and end values will be
+            the same.
+        """
         if self.direction == 'horizontal':
             vmin = self._selection_artist.get_x()
             vmax = vmin + self._selection_artist.get_width()