Fix errors in LinkHelper and LinkInlineParser.

src/Markdig.Tests/TestLinkHelper.cs

@@ -89,6 +89,14 @@ public void TestTitleMultiline()
         Assert.AreEqual("this\ris\r\na\ntitle", title);
     }
 
+    [Test]
+    public void TestTitleMultilineWithSpaceAndBackslash()
+    {
+        var text = new StringSlice("'a\n\\ \\\ntitle'");
+        Assert.True(LinkHelper.TryParseTitle(ref text, out string title, out _));
+        Assert.AreEqual("a\n\\ \\\ntitle", title);
+    }
+
     [Test]
     public void TestUrlAndTitle()
     {
@@ -238,6 +246,13 @@ public void TestlLinkReferenceDefinitionSimple()
 
     }
 
+    [Test]
+    public void TestlLinkReferenceDefinitionInvalid()
+    {
+        var text = new StringSlice("[foo]: /url (title) x\n");
+        Assert.False(LinkHelper.TryParseLinkReferenceDefinition(ref text, out _, out _, out _, out _, out _, out _));
+    }
+
     [Test]
     public void TestAutoLinkUrlSimple()
     {

src/Markdig.Tests/TestPlayParser.cs

@@ -46,6 +46,14 @@ public void TestLink()
         Assert.AreEqual("/yoyo", link?.Url);
     }
 
+    [Test]
+    public void TestLinkWithMultipleBackslashesInTitle()
+    {
+        var doc = Markdown.Parse(@"[link](/uri '\\\\127.0.0.1')");
+        var link = doc.Descendants<ParagraphBlock>().SelectMany(x => x.Inline.Descendants<LinkInline>()).FirstOrDefault();
+        Assert.AreEqual(@"\\127.0.0.1", link?.Title);
+    }
+
     [Test]
     public void TestListBug2()
     {