Re: [PATCH 1/5] chainlint: match arbitrary here-docs tags rather than hard-coded names

diff --git a/t/chainlint.sed b/t/chainlint.sed
index 5f0882cb38..bd76c5d181 100644
--- a/t/chainlint.sed
+++ b/t/chainlint.sed

@@ -61,6 +61,22 @@
 # "else", and "fi" in if-then-else likewise must not end with "&&", thus
 # receives similar treatment.
 #
+# Swallowing here-docs with arbitrary tags requires a bit of finesse. When a
+# line such as "cat <<EOF >out" is seen, the here-doc tag is moved to the front
+# of the line enclosed in angle brackets as a sentinel, giving "<EOF>cat >out".
+# As each subsequent line is read, it is appended to the target line and a
+# (whitespace-loose) back-reference match /^<(.*)>\n\1$/ is attempted to see if
+# the content inside "<...>" matches the entirety of the newly-read line. For
+# instance, if the next line read is "some data", when concatenated with the
+# target line, it becomes "<EOF>cat >out\nsome data", and a match is attempted
+# to see if "EOF" matches "some data". Since it doesn't, the next line is
+# attempted. When a line consisting of only "EOF" (and possible whitespace) is
+# encountered, it is appended to the target line giving "<EOF>cat >out\nEOF",
+# in which case the "EOF" inside "<...>" does match the text following the
+# newline, thus the closing here-doc tag has been found. The closing tag line
+# and the "<...>" prefix on the target line are then discarded, leaving just
+# the target line "cat >out".