diff -r 0471b9ddd0b2 -r 844b1ad5b34b README
--- a/README	Wed Apr 08 01:17:01 2020 +0800
+++ b/README	Fri May 08 22:50:09 2020 +0800
@@ -139,20 +139,32 @@
     $ cd tests
     $ python $HGSRC/tests/run-tests.py
 
+When certain blocks of code need to cope with API changes in core Mercurial,
+they should have comments in the ``hg <= x.y (commit hash)`` format. For
+example, if a function needs another code path because of changes introduced in
+02802fa87b74 that was first included in Mercurial 5.3, then the comment should
+be::
+
+    # hg <= 5.2 (02802fa87b74)
+
+See also tests/test-check-compat-strings.t.
+
 Branch policy
 -------------
 
-The evolve test are highly impacted by changes in core. To deal with this, we use named branches.
+The evolve tests are highly impacted by changes in core. To deal with this, we
+use named branches.
 
-There are two main branches: "stable" and "default". Tests on these branch are
-supposed to pass with the corresponding "default" and "stable" branch from core
-Mercurial. The documentation is built from the tip of stable.
+There are two main branches: "stable" and "default". Tests on these branches
+are supposed to pass with the corresponding "default" and "stable" branch from
+core Mercurial. The documentation is built from the tip of stable.
 
-In addition, we have compatibility branches to check tests on older version of
+In addition, we have compatibility branches to check tests on older versions of
 Mercurial. They are the "mercurial-x.y" branches. They are used to apply
-expected test change only, no code change should happen there.
+expected test changes only, no code changes should happen there.
 
-test output change from a changeset in core should adds the following line to their description:
+Test output changes from a changeset in core should add the following line to
+their patch description:
 
 CORE-TEST-OUTPUT-UPDATE: <CORE-NODE-ID>