diff --git a/src/Noted/Core/Models/EpubXPathLocation.cs b/src/Noted/Core/Models/EpubXPathLocation.cs
index 920b405..4e4b31e 100644
--- a/src/Noted/Core/Models/EpubXPathLocation.cs
+++ b/src/Noted/Core/Models/EpubXPathLocation.cs
@@ -6,7 +6,7 @@ namespace Noted.Core.Models;
 using System;
 using System.Text.RegularExpressions;
 
-public struct EpubXPathLocation(string pos0, string pos1) : IComparable
+public readonly struct EpubXPathLocation(string pos0, string pos1) : IComparable
 {
     public EpubLocation Start { get; init; } = EpubLocation.FromString(pos0);
 
@@ -18,9 +18,9 @@ public static EpubXPathLocation FromString(string location)
         return new EpubXPathLocation(range[0], range[1]);
     }
 
-    public override string ToString() => $"epubxpath://{this.Start}-{this.End}";
+    public override readonly string ToString() => $"epubxpath://{this.Start}-{this.End}";
 
-    public int CompareTo(object? obj)
+    public readonly int CompareTo(object? obj)
     {
         if (obj is not EpubXPathLocation other)
         {
diff --git a/test/Noted.Tests/Extensions/Readers/Common/HtmlSectionParserTests.cs b/test/Noted.Tests/Extensions/Readers/Common/HtmlSectionParserTests.cs
index 5fda9ef..dcf1f18 100644
--- a/test/Noted.Tests/Extensions/Readers/Common/HtmlSectionParserTests.cs
+++ b/test/Noted.Tests/Extensions/Readers/Common/HtmlSectionParserTests.cs
@@ -3,17 +3,17 @@
 
 namespace Noted.Tests.Extensions.Readers.Common
 {
-  using System.IO;
-  using System.Linq;
-  using System.Text;
-  using System.Threading.Tasks;
-  using Microsoft.VisualStudio.TestTools.UnitTesting;
-  using Noted.Extensions.Readers.Common;
+    using System.IO;
+    using System.Linq;
+    using System.Text;
+    using System.Threading.Tasks;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+    using Noted.Extensions.Readers.Common;
 
-  [TestClass]
-  public class HtmlSectionParserTests
-  {
-    private const string TocFragment = @"
+    [TestClass]
+    public class HtmlSectionParserTests
+    {
+        private const string TocFragment = @"
 <p height=""1em"" width=""0pt"" align=""center"">
   <font size=""5"">
     <b>Table of Contents</b>
@@ -59,44 +59,44 @@ public class HtmlSectionParserTests
 <mbp:pagebreak/>
 ";
 
-    private readonly HtmlSectionParser parser;
+        private readonly HtmlSectionParser parser;
 
-    public HtmlSectionParserTests()
-    {
-      this.parser = new HtmlSectionParser();
-    }
+        public HtmlSectionParserTests()
+        {
+            this.parser = new HtmlSectionParser();
+        }
 
-    [TestMethod]
-    public async Task ParseShouldReturnTableOfContentWithDepth()
-    {
-      await using var stream = new MemoryStream(Encoding.UTF8.GetBytes(TocFragment));
-      var toc = await HtmlSectionParser.Parse(stream).ToListAsync();
+        [TestMethod]
+        public async Task ParseShouldReturnTableOfContentWithDepth()
+        {
+            await using var stream = new MemoryStream(Encoding.UTF8.GetBytes(TocFragment));
+            var toc = await HtmlSectionParser.Parse(stream).ToListAsync();
 
-      Assert.AreEqual(11, toc.Count);
-      Assert.AreEqual("Preface", toc[0].Title);
-      Assert.AreEqual(1, toc[0].Level);
-      Assert.AreEqual(3859, toc[0].Location);
-      Assert.AreEqual("Section 1.1", toc[4].Title);
-      Assert.AreEqual(2, toc[4].Level);
-      Assert.AreEqual(21076, toc[4].Location);
-      Assert.AreEqual("Section 1.1.1", toc[5].Title);
-      Assert.AreEqual(3, toc[5].Level);
-      Assert.AreEqual("Section 1.2", toc[6].Title);
-      Assert.AreEqual(2, toc[6].Level);
-    }
+            Assert.AreEqual(11, toc.Count);
+            Assert.AreEqual("Preface", toc[0].Title);
+            Assert.AreEqual(1, toc[0].Level);
+            Assert.AreEqual(3859, toc[0].Location);
+            Assert.AreEqual("Section 1.1", toc[4].Title);
+            Assert.AreEqual(2, toc[4].Level);
+            Assert.AreEqual(21076, toc[4].Location);
+            Assert.AreEqual("Section 1.1.1", toc[5].Title);
+            Assert.AreEqual(3, toc[5].Level);
+            Assert.AreEqual("Section 1.2", toc[6].Title);
+            Assert.AreEqual(2, toc[6].Level);
+        }
 
-    [TestMethod]
-    public async Task ParseShouldCreateDocumentSectionRelationships()
-    {
-      await using var stream = new MemoryStream(Encoding.UTF8.GetBytes(TocFragment));
-      var toc = await HtmlSectionParser.Parse(stream).ToListAsync();
+        [TestMethod]
+        public async Task ParseShouldCreateDocumentSectionRelationships()
+        {
+            await using var stream = new MemoryStream(Encoding.UTF8.GetBytes(TocFragment));
+            var toc = await HtmlSectionParser.Parse(stream).ToListAsync();
 
-      Assert.AreEqual(null, toc[3].Parent);     // 1 -> null
-      Assert.AreEqual("Section 1.1", toc[4].Title);
-      Assert.AreEqual(toc[3], toc[4].Parent);   // 1.1 -> 1
-      Assert.AreEqual(toc[4], toc[5].Parent);   // 1.1.1 -> 1.1
-      Assert.AreEqual(toc[3], toc[6].Parent);   // 1.2 -> 1
-      Assert.AreEqual(null, toc[7].Parent);     // 2 -> null
+            Assert.AreEqual(null, toc[3].Parent);     // 1 -> null
+            Assert.AreEqual("Section 1.1", toc[4].Title);
+            Assert.AreEqual(toc[3], toc[4].Parent);   // 1.1 -> 1
+            Assert.AreEqual(toc[4], toc[5].Parent);   // 1.1.1 -> 1.1
+            Assert.AreEqual(toc[3], toc[6].Parent);   // 1.2 -> 1
+            Assert.AreEqual(null, toc[7].Parent);     // 2 -> null
+        }
     }
-  }
 }
\ No newline at end of file