Add comments to code.

Utility.Guard/Guard.cs

@@ -2,8 +2,18 @@
 
 namespace Utility;
 
+/// <summary>
+/// Provides guard clauses for validating method arguments.
+/// </summary>
 public static class Guard
 {
+    /// <summary>
+    /// Throws an <see cref="InvalidOperationException"/> if the specified item is null.
+    /// </summary>
+    /// <typeparam name="T">The type of the item.</typeparam>
+    /// <param name="item">The item to check for null.</param>
+    /// <returns>The original item if it is not null.</returns>
+    /// <exception cref="InvalidOperationException">Thrown if the item is null.</exception>
     public static T ThrowIfNull<T>(T item)
     {
         if (item is null)
@@ -14,6 +24,13 @@ public static T ThrowIfNull<T>(T item)
         return item;
     }
 
+    /// <summary>
+    /// Throws an <see cref="InvalidOperationException"/> if the specified item is not null.
+    /// </summary>
+    /// <typeparam name="T">The type of the item.</typeparam>
+    /// <param name="item">The item to check for not null.</param>
+    /// <returns>The original item if it is null.</returns>
+    /// <exception cref="InvalidOperationException">Thrown if the item is not null.</exception>
     public static T ThrowIfNotNull<T>(T item)
     {
         if (item is not null)
@@ -24,6 +41,14 @@ public static T ThrowIfNotNull<T>(T item)
         return item;
     }
 
+    /// <summary>
+    /// Throws an <see cref="InvalidOperationException"/> if the specified integer is within the specified range.
+    /// </summary>
+    /// <param name="item">The integer to check.</param>
+    /// <param name="start">The start of the range.</param>
+    /// <param name="end">The end of the range.</param>
+    /// <returns>The original integer if it is not within the range.</returns>
+    /// <exception cref="InvalidOperationException">Thrown if the integer is within the range.</exception>
     public static int ThrowIfIntegerNotInRange(int item, int start, int end)
     {
         if (item >= start && item <= end)
@@ -34,6 +59,12 @@ public static int ThrowIfIntegerNotInRange(int item, int start, int end)
         return item;
     }
 
+    /// <summary>
+    /// Throws an <see cref="InvalidOperationException"/> if the specified string is null or empty.
+    /// </summary>
+    /// <param name="value">The string to check.</param>
+    /// <returns>The original string if it is not null or empty.</returns>
+    /// <exception cref="InvalidOperationException">Thrown if the string is null or empty.</exception>
     public static string ThrowIfStringNullOrEmpty(string value)
     {
         if (string.IsNullOrEmpty(value))