From 113ac67890fb90be2f66270cf341dde983cbb875 Mon Sep 17 00:00:00 2001
From: Michael Howell <michael@notriddle.com>
Date: Fri, 26 Jan 2024 16:59:13 -0700
Subject: [PATCH] Match HTML declaration blocks with lowercase letters

---
 commonmark/src/Commonmark/Blocks.hs |  8 ++++++--
 commonmark/test/regression.md       | 14 ++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/commonmark/src/Commonmark/Blocks.hs b/commonmark/src/Commonmark/Blocks.hs
index f3a8ee1..2cf27bd 100644
--- a/commonmark/src/Commonmark/Blocks.hs
+++ b/commonmark/src/Commonmark/Blocks.hs
@@ -61,7 +61,7 @@ import           Control.Monad             (foldM, guard, mzero, void, unless,
                                             when)
 import           Control.Monad.Trans.Class (lift)
 import           Data.Foldable             (foldrM)
-import           Unicode.Char              (isAsciiUpper, isDigit)
+import           Unicode.Char              (isAsciiUpper, isAsciiLower, isDigit)
 import           Unicode.Char.General.Compat (isSpace)
 import           Data.Dynamic
 import           Data.Text                 (Text)
@@ -1165,7 +1165,7 @@ startCond 3 = void $ symbol '?'
 startCond 4 = void $ try $ do
   symbol '!'
   satisfyWord (\t -> case T.uncons t of
-                          Just (c, _) -> isAsciiUpper c
+                          Just (c, _) -> isAsciiLetter c
                           _           -> False)
 startCond 5 = void $ try $ do
   symbol '!'
@@ -1231,6 +1231,10 @@ removeConsecutive (x:y:zs)
   | x == y + 1 = removeConsecutive (y:zs)
 removeConsecutive xs = xs
 
+isAsciiLetter :: Char -> Bool
+isAsciiLetter c =
+  isAsciiUpper c || isAsciiLower c
+
 -------------------------------------------------------------------------
 
 collapseNodeStack :: [BlockNode m il bl] -> BlockParser m il bl (BlockNode m il bl)
diff --git a/commonmark/test/regression.md b/commonmark/test/regression.md
index fa6a9c3..c17bf83 100644
--- a/commonmark/test/regression.md
+++ b/commonmark/test/regression.md
@@ -336,3 +336,17 @@ Test <span> x <span>
 <p>Test <span> <span></p>
 <p>Test <span> x <span></p>
 ````````````````````````````````
+
+
+Issue #142
+```````````````````````````````` example
+<!X
+>
+<!x
+>
+.
+<!X
+>
+<!x
+>
+````````````````````````````````