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diff --git a/src/linker/Linker/ILParameterIndex.cs b/src/linker/Linker/ILParameterIndex.cs
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+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Mono.Linker
+{
+	/// <summary>
+	/// Represents the index of arguments passed to a function in IL (i.e. (ILParameterIndex)0 represents `this` for non-static methods.
+	/// This is used to enforce a differentiation between scenarios where the 0 index should be `this` and when the 0 index should be the first non-this parameter in the type system.
+	/// There are no named enum values, the underlying integer value represents the index value.
+	/// Generally prefer to use <see cref="ILLink.Shared.SourceParameterIndex"/> when possible.
+	/// See also <seealso cref="Mono.Linker.ParameterHelpers"/>.
+	/// </summary>
+	/// <example>
+	/// In a call to a non-static function Foo(int a, int b, int c)
+	/// 0 refers to `this`,
+	/// 1 refers to a,
+	/// 2 refers to b.
+	/// 3 referes to c.
+	/// </example>
+	public enum ILParameterIndex
+	{ }
+}