diff --git a/docs/john_gruber.md b/docs/john_gruber.md
index e2011e0..fa554b1 100644
--- a/docs/john_gruber.md
+++ b/docs/john_gruber.md
@@ -14,3 +14,10 @@ level 7 headings)
 
 But there are also "Setext-style headers" that can only create \
 level 1 and 2 headers.
+
+> Any number of underlining =’s or -’s will work.
+
+`bat` does not detect "setext" at all.\
+`vim` interprets a line that is followed by a line with at least one \
+`=` or `-` as a header. (that line may not include any other characters than \
+`-` or `=` and they may not be mixed)