--- a/hgext3rd/evolve/obshistory.py	Fri May 01 07:44:01 2020 -0700
+++ b/hgext3rd/evolve/obshistory.py	Sat Apr 25 18:51:23 2020 +0800
@@ -209,6 +209,11 @@
         pass
 
 def patchavailable(node, repo, candidates, successive=True):
+    """ Check if it's possible to get a diff between node and candidates.
+
+    `candidates` contains nodes, which can be either successors (`successive`
+    is True) or predecessors (`successive` is False) of `node`.
+    """
     if node not in repo:
         return False, b"context is not local"