diff --git a/strings-csharp/CaseInsensitiveSubstringSearch/BenchmarkRunner/BenchmarkRunner.csproj b/strings-csharp/CaseInsensitiveSubstringSearch/BenchmarkRunner/BenchmarkRunner.csproj
index 083757afe1..46ec814a74 100644
--- a/strings-csharp/CaseInsensitiveSubstringSearch/BenchmarkRunner/BenchmarkRunner.csproj
+++ b/strings-csharp/CaseInsensitiveSubstringSearch/BenchmarkRunner/BenchmarkRunner.csproj
@@ -2,13 +2,13 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.13.8" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.15.8" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch.csproj b/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch.csproj
index f02677bf64..dfb40caafc 100644
--- a/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch.csproj
+++ b/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/SubstringSearch.cs b/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/SubstringSearch.cs
index db8b1143a9..cda2b1cd08 100644
--- a/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/SubstringSearch.cs
+++ b/strings-csharp/CaseInsensitiveSubstringSearch/CaseInsensitiveSubstringSearch/SubstringSearch.cs
@@ -28,13 +28,20 @@ public static bool StringToUpperInvariant(string sourceString, string substringT
         }
 
         // Regular Expression Search
+        // Regex.Escape() treats the search term as literal text, so a term such as "c.de" or "z*"
+        // is not reinterpreted as a pattern and an unmatched bracket does not throw.
+        // RegexOptions.CultureInvariant keeps IgnoreCase off the current culture's casing rules.
         public static bool RegexIsMatch(string sourceString, string substringToSearch)
         {
             return Regex
-                .IsMatch(sourceString, substringToSearch, RegexOptions.IgnoreCase);
+                .IsMatch(sourceString,
+                    Regex.Escape(substringToSearch),
+                    RegexOptions.IgnoreCase | RegexOptions.CultureInvariant);
         }
 
         // Linq With String Equals Method Search
+        // This matches whole separator-delimited words, not substrings, so it answers a different
+        // question from the other four methods. That difference is intentional, not a bug.
         public static bool LinqStringEquals(string sourceString, string substringToSearch, char separator)
         {
             return sourceString
diff --git a/strings-csharp/CaseInsensitiveSubstringSearch/Tests/SubstringSearchSemanticsTest.cs b/strings-csharp/CaseInsensitiveSubstringSearch/Tests/SubstringSearchSemanticsTest.cs
new file mode 100644
index 0000000000..92daa4363a
--- /dev/null
+++ b/strings-csharp/CaseInsensitiveSubstringSearch/Tests/SubstringSearchSemanticsTest.cs
@@ -0,0 +1,60 @@
+using System.Globalization;
+using CaseInsensitiveSubstringSearch;
+
+namespace Tests
+{
+    [TestClass]
+    public class SubstringSearchSemanticsTest
+    {
+        private const string SourceString = "Code Maze";
+
+        [TestMethod]
+        [DataRow("aze")]
+        [DataRow("ode")]
+        [DataRow("e M")]
+        public void GivenMidWordSubstring_WhenComparingAllFiveMethods_ThenOnlyLinqStringEqualsReturnsFalse(string subStringToSearch)
+        {
+            Assert.IsTrue(SubstringSearch.StringContains(SourceString, subStringToSearch));
+            Assert.IsTrue(SubstringSearch.StringIndexOf(SourceString, subStringToSearch));
+            Assert.IsTrue(SubstringSearch.StringToUpperInvariant(SourceString, subStringToSearch));
+            Assert.IsTrue(SubstringSearch.RegexIsMatch(SourceString, subStringToSearch));
+
+            Assert.IsFalse(SubstringSearch.LinqStringEquals(SourceString, subStringToSearch, ' '));
+        }
+
+        [TestMethod]
+        [DataRow("c.de")]
+        [DataRow("z*")]
+        [DataRow("m|q")]
+        [DataRow("(")]
+        public void GivenSearchTermHoldingRegexMetacharacters_WhenUsingRegexIsMatchMethod_ThenItAgreesWithStringContains(string subStringToSearch)
+        {
+            var expectedResult = SubstringSearch.StringContains(SourceString, subStringToSearch);
+
+            var result = SubstringSearch.RegexIsMatch(SourceString, subStringToSearch);
+
+            Assert.AreEqual(expectedResult, result);
+            Assert.IsFalse(result);
+        }
+
+        [TestMethod]
+        public void GivenTurkishCulture_WhenSearchingForFileInsideFILE_ThenAllFourContainmentMethodsMatch()
+        {
+            var originalCulture = CultureInfo.CurrentCulture;
+
+            try
+            {
+                CultureInfo.CurrentCulture = new CultureInfo("tr-TR");
+
+                Assert.IsTrue(SubstringSearch.StringContains("FILE", "file"));
+                Assert.IsTrue(SubstringSearch.StringIndexOf("FILE", "file"));
+                Assert.IsTrue(SubstringSearch.StringToUpperInvariant("FILE", "file"));
+                Assert.IsTrue(SubstringSearch.RegexIsMatch("FILE", "file"));
+            }
+            finally
+            {
+                CultureInfo.CurrentCulture = originalCulture;
+            }
+        }
+    }
+}
diff --git a/strings-csharp/CaseInsensitiveSubstringSearch/Tests/Tests.csproj b/strings-csharp/CaseInsensitiveSubstringSearch/Tests/Tests.csproj
index fbf6af0b48..a75aead610 100644
--- a/strings-csharp/CaseInsensitiveSubstringSearch/Tests/Tests.csproj
+++ b/strings-csharp/CaseInsensitiveSubstringSearch/Tests/Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -9,10 +9,10 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
-    <PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
-    <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
-    <PackageReference Include="coverlet.collector" Version="3.1.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="4.4.0" />
+    <PackageReference Include="MSTest.TestFramework" Version="4.4.0" />
+    <PackageReference Include="coverlet.collector" Version="10.0.1" />
   </ItemGroup>
 
   <ItemGroup>