diff -r 0c09afdf5704 -r 19b9fc40cc51 mercurial/help/internals/revlogs.txt
--- a/mercurial/help/internals/revlogs.txt	Tue Jun 06 08:58:27 2017 -0700
+++ b/mercurial/help/internals/revlogs.txt	Fri May 19 20:29:11 2017 -0700
@@ -45,6 +45,12 @@
 1
    RevlogNG (*next generation*). It replaced version 0 when it was
    implemented in 2006.
+2
+   In-development version incorporating accumulated knowledge and
+   missing features from 10+ years of revlog version 1.
+57005 (0xdead)
+   Reserved for internal testing of new versions. No defined format
+   beyond 32-bit header.
 
 The feature flags short consists of bit flags. Where 0 is the least
 significant bit, the following bit offsets define flags:
@@ -142,6 +148,14 @@
 The first 4 bytes of the revlog are shared between the revlog header
 and the 6 byte absolute offset field from the first revlog entry.
 
+Version 2 Format
+================
+
+(In development. Format not finalized or stable.)
+
+Version 2 is currently identical to version 1. This will obviously
+change.
+
 Delta Chains
 ============