diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
index 75d0775dce7f49c21fd5ca3a4c468566a4950c11_bWVyY3VyaWFsL2RlYnVnY29tbWFuZHMucHk=..e7d23c512d3d40a0850100dbbd57b77e92922caa_bWVyY3VyaWFsL2RlYnVnY29tbWFuZHMucHk= 100644
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -764,6 +764,12 @@
     :``chainlen``:  delta chain length to this revision
     :``prevrev``:   previous revision in delta chain
     :``deltatype``: role of delta / how it was computed
+                    - base:  a full snapshot
+                    - snap:  an intermediate snapshot
+                    - p1:    a delta against the first parent
+                    - p2:    a delta against the second parent
+                    - prev:  a delta against the previous revision
+                    - other: a delta against an arbitrary revision
     :``compsize``:  compressed size of revision
     :``uncompsize``: uncompressed size of revision
     :``chainsize``: total size of compressed revisions in chain