Add caseSensitive parameter on the InlineSyntax constructor (dart-lang/markdown#400)

pkgs/markdown/lib/src/inline_parser.dart

diff --git a/pkgs/markdown/lib/src/inline_parser.dart b/pkgs/markdown/lib/src/inline_parser.dart
index e9c5f84..954e605 100644
--- a/pkgs/markdown/lib/src/inline_parser.dart
+++ b/pkgs/markdown/lib/src/inline_parser.dart
@@ -351,8 +351,12 @@
   ///
   /// If [startCharacter] is passed, it is used as a pre-matching check which
   /// is faster than matching against [pattern].
-  InlineSyntax(String pattern, {int? startCharacter})
-      : pattern = RegExp(pattern, multiLine: true),
+  ///
+  /// If [caseSensitive] is disabled, then case is ignored when matching
+  /// the [pattern].
+  InlineSyntax(String pattern, {int? startCharacter, bool caseSensitive = true})
+      : pattern =
+            RegExp(pattern, multiLine: true, caseSensitive: caseSensitive),
         _startCharacter = startCharacter;
 
   /// Tries to match at the parser's current position.

pkgs/markdown/test/html_renderer_test.dart

diff --git a/pkgs/markdown/test/html_renderer_test.dart b/pkgs/markdown/test/html_renderer_test.dart
index d478fc7..35ac762 100644
--- a/pkgs/markdown/test/html_renderer_test.dart
+++ b/pkgs/markdown/test/html_renderer_test.dart
@@ -77,4 +77,39 @@
       );
     });
   });
+
+  group('test InlineSyntax caseSensitive parameter', () {
+    const text = 'one BREAK two';
+
+    test('with caseSensitive enabled', () {
+      final result = markdownToHtml(
+        text,
+        inlineOnly: true,
+        inlineSyntaxes: [_BreakSyntax(true)],
+      );
+
+      expect(result, equals('one BREAK two'));
+    });
+
+    test('with caseSensitive disabled', () {
+      final result = markdownToHtml(
+        text,
+        inlineOnly: true,
+        inlineSyntaxes: [_BreakSyntax(false)],
+      );
+
+      expect(result, equals('one <break /> two'));
+    });
+  });
+}
+
+class _BreakSyntax extends InlineSyntax {
+  _BreakSyntax(bool caseSensitive)
+      : super('break', caseSensitive: caseSensitive);
+
+  @override
+  bool onMatch(InlineParser parser, Match match) {
+    parser.addNode(Element.empty('break'));
+    return true;
+  }
 }