fix: Update GFM alert regex to disallow content on header line

CHANGELOG.md

@@ -1,3 +1,10 @@
+## v2.2.2(2026-01-05)
+
+### Fixed
+
+- Fix a bug in GFM alert block parsing where alert types were case-sensitive.
+- Fix GFM alert regex to disallow content on header line.
+
 ## v2.2.1(2025-10-13)
 
 ### Changed

marko/__init__.py

@@ -23,7 +23,7 @@
     from .block import Document
     from .parser import ElementType
 
-__version__ = "2.2.1"
+__version__ = "2.2.2"
 
 
 class SetupDone(Exception):

marko/ext/gfm/elements.py

@@ -225,11 +225,13 @@ class Alert(block.Quote):
 
     @classmethod
     def match(cls, source):
-        return source.expect_re(r" {,3}>\s*\[\!(WARNING|NOTE|TIP|IMPORTANT|CAUTION)\]")
+        return source.expect_re(
+            r"(?im) {,3}>\s*\[\!(WARNING|NOTE|TIP|IMPORTANT|CAUTION)\]\s*$"
+        )
 
     @classmethod
     def parse(cls, source):
-        alert_type = source.match.group(1)
+        alert_type = source.match.group(1).upper()
         source.next_line(require_prefix=False)
         source.consume()
         state = cls(alert_type)

tests/test_ext.py

@@ -1,3 +1,5 @@
+import pytest
+
 from marko import Markdown
 
 
@@ -106,20 +108,32 @@ def setup_method(self):
         self.md_ast = Markdown(renderer=ASTRenderer, extensions=[GFM])
         self.md_html = Markdown(extensions=[GFM])
 
-    def test_alert_ast(self):
-        text = "> [!WARNING]\n> Foo bar\n> Bar\n"
+    @pytest.mark.parametrize(
+        "alert_type", ["WARNING", "CAUTION", "TIP", "warning", "Caution"]
+    )
+    def test_alert_ast(self, alert_type):
+        text = f"> [!{alert_type}]\n> Foo bar\n> Bar\n"
         ast = self.md_ast(text)
         admon = ast["children"][0]
         assert admon["element"] == "alert"
-        assert admon["alert_type"] == "WARNING"
+        assert admon["alert_type"] == alert_type.upper()
         inner = admon["children"][0]["children"]
         assert inner[0]["children"] == "Foo bar"
         assert inner[1]["element"] == "line_break"
         assert inner[2]["children"] == "Bar"
 
-    def test_alert_html(self):
-        text = "> [!WARNING]\n> Foo bar\n> Bar\n"
+    @pytest.mark.parametrize(
+        "alert_type", ["WARNING", "CAUTION", "TIP", "warning", "Caution"]
+    )
+    def test_alert_html(self, alert_type):
+        text = f"> [!{alert_type}]\n> Foo bar\n> Bar\n"
         html = self.md_html(text)
-        assert '<blockquote class="alert alert-warning">' in html
-        assert "<p>Warning</p>" in html
+        assert f'<blockquote class="alert alert-{alert_type.lower()}">' in html
+        assert f"<p>{alert_type.title()}</p>" in html
         assert "<p>Foo bar\nBar</p>" in html
+
+    def test_alert_disallow_content_on_header_line(self):
+        text = "> [!NOTE] This is not allowed.\n> Foo bar\n"
+        html = self.md_html(text)
+        # Should be treated as a normal blockquote.
+        assert "<blockquote>\n<p>[!NOTE] This is not allowed." in html