Backport PR matplotlib#29617: DOC: Add docstrings to matplotlib.cbook.GrouperView (matplotlib#29627)

Co-authored-by: Christine P. Chai <star1327p@gmail.com>

Author: meeseeksmachine

lib/matplotlib/cbook.py

@@ -880,8 +880,18 @@ class GrouperView:
     def __init__(self, grouper): self._grouper = grouper
     def __contains__(self, item): return item in self._grouper
     def __iter__(self): return iter(self._grouper)
-    def joined(self, a, b): return self._grouper.joined(a, b)
-    def get_siblings(self, a): return self._grouper.get_siblings(a)
+
+    def joined(self, a, b):
+        """
+        Return whether *a* and *b* are members of the same set.
+        """
+        return self._grouper.joined(a, b)
+
+    def get_siblings(self, a):
+        """
+        Return all of the items joined with *a*, including itself.
+        """
+        return self._grouper.get_siblings(a)
 
 
 def simple_linear_interpolation(a, steps):