Fragment no longer opens on a blank line

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;NU1608;NU1109</NoWarn>
-    <Version>5.1.1</Version>
+    <Version>5.1.2</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <LangVersion>preview</LangVersion>
     <PackageTags>AngleSharp, Verify</PackageTags>

src/Tests/PrettyPrintHtmlTests.FragmentDoesNotOpenWithABlankLine.verified.html

@@ -0,0 +1 @@
+<p>My first paragraph.</p>

src/Tests/PrettyPrintHtmlTests.FragmentIsNotWrappedInDocument.verified.html

@@ -1,2 +1 @@
-
-<p>My first paragraph.</p>
+<p>My first paragraph.</p>

src/Tests/PrettyPrintHtmlTests.PreservesPreformattedText.verified.html

@@ -1,5 +1,4 @@
-
-<div>
+<div>
   <pre>SELECT [e].[Name]
 FROM [Employees] AS [e]
 WHERE [e].[Active] = 1</pre>

src/Tests/PrettyPrintHtmlTests.PreservesTextareaAndScript.verified.html

@@ -1,5 +1,4 @@
-
-<div>
+<div>
   <textarea>line one
 line two</textarea>
   <script>

src/Tests/PrettyPrintHtmlTests.TableCellFragment.verified.html

@@ -1,3 +1,2 @@
-
-<td>Aaron</td>
+<td>Aaron</td>
 <td>FullTime</td>

src/Tests/PrettyPrintHtmlTests.TableFragmentBehindAComment.verified.html

@@ -1,5 +1,4 @@
-
-<!--marker-->
+<!--marker-->
 <thead>
   <tr>
     <th>Name</th>

src/Tests/PrettyPrintHtmlTests.TableRowFragment.verified.html

@@ -1,5 +1,4 @@
-
-<tr>
+<tr>
   <td>Aaron</td>
   <td>FullTime</td>
 </tr>

src/Tests/PrettyPrintHtmlTests.TableSectionFragment.verified.html

@@ -1,5 +1,4 @@
-
-<thead>
+<thead>
   <tr>
     <th>Name</th>
   </tr>

src/Tests/PrettyPrintHtmlTests.cs

@@ -128,4 +128,34 @@ public Task FragmentOpeningWithText()
         return Verify(html, "html")
             .PrettyPrintHtml();
     }
+
+    // A fragment is parsed against a context element that is never written, and the formatter breaks
+    // the line before every node inside an element. So the first node took a break with nothing in
+    // front of it and the markup opened on the second line.
+    //
+    // Compared as text rather than by the registered html comparer: that one diffs the two DOMs, where
+    // a blank line before the first node is whitespace between nodes and no difference at all. Every
+    // other test here is blind to the thing this one is for.
+    [Test]
+    public Task FragmentDoesNotOpenWithABlankLine()
+    {
+        var html = "<p>My first paragraph.</p>";
+        return Verify(html, "html")
+            .PrettyPrintHtml()
+            .UseStringComparer(CompareText);
+    }
+
+    static Task<VerifyTests.CompareResult> CompareText(
+        string received,
+        string verified,
+        IReadOnlyDictionary<string, object> context)
+    {
+        if (string.Equals(received, verified, StringComparison.Ordinal))
+        {
+            return Task.FromResult(VerifyTests.CompareResult.Equal);
+        }
+
+        return Task.FromResult(
+            VerifyTests.CompareResult.NotEqual($"Received:{Environment.NewLine}{received}"));
+    }
 }

src/Verify.AngleSharp/HtmlPrettyPrint.cs

@@ -313,12 +313,30 @@ static void CleanSource(StringBuilder builder, Action<INodeList>? action)
             document.ToHtml(writer, formatter);
         }
 
+        TrimLeadingNewLine(builder);
+
         for (var index = 0; index < preserved.Count; index++)
         {
             builder.Replace(Placeholder(index), preserved[index]);
         }
     }
 
+    /// <summary>
+    /// The formatter breaks the line before every node that sits inside an element, to part it from
+    /// whatever came before. A fragment is parsed against a context element that is never itself
+    /// written, so its first node takes that break with nothing in front of it and the markup opens on
+    /// the second line. A document has no such context, and a fragment opening with text is not broken
+    /// before either, so in those cases there is nothing here to remove.
+    /// </summary>
+    static void TrimLeadingNewLine(StringBuilder builder)
+    {
+        if (builder.Length > 0 &&
+            builder[0] == '\n')
+        {
+            builder.Remove(0, 1);
+        }
+    }
+
     /// <summary>
     /// Swaps the content of each preformatted element for a placeholder, returning the markup each
     /// stood for. The element keeps its place, so the document is laid out exactly as it would have