diff --git a/src/Mvc/Mvc.Core/ref/Microsoft.AspNetCore.Mvc.Core.netcoreapp3.0.cs b/src/Mvc/Mvc.Core/ref/Microsoft.AspNetCore.Mvc.Core.netcoreapp3.0.cs
index a895709b24..ce0bbc1f92 100644
--- a/src/Mvc/Mvc.Core/ref/Microsoft.AspNetCore.Mvc.Core.netcoreapp3.0.cs
+++ b/src/Mvc/Mvc.Core/ref/Microsoft.AspNetCore.Mvc.Core.netcoreapp3.0.cs
@@ -1270,6 +1270,14 @@ namespace Microsoft.AspNetCore.Mvc.ActionConstraints
         public bool Accept(Microsoft.AspNetCore.Mvc.ActionConstraints.ActionConstraintContext context) { throw null; }
         public abstract bool IsValidForRequest(Microsoft.AspNetCore.Routing.RouteContext routeContext, Microsoft.AspNetCore.Mvc.Abstractions.ActionDescriptor action);
     }
+    public partial class HttpMethodActionConstraint : Microsoft.AspNetCore.Mvc.ActionConstraints.IActionConstraint, Microsoft.AspNetCore.Mvc.ActionConstraints.IActionConstraintMetadata
+    {
+        public static readonly int HttpMethodConstraintOrder;
+        public HttpMethodActionConstraint(System.Collections.Generic.IEnumerable<string> httpMethods) { }
+        public System.Collections.Generic.IEnumerable<string> HttpMethods { get { throw null; } }
+        public int Order { get { throw null; } }
+        public virtual bool Accept(Microsoft.AspNetCore.Mvc.ActionConstraints.ActionConstraintContext context) { throw null; }
+    }
 }
 namespace Microsoft.AspNetCore.Mvc.ApiExplorer
 {
@@ -1941,6 +1949,11 @@ namespace Microsoft.AspNetCore.Mvc.Infrastructure
     {
         public ActionResultStatusCodeAttribute() { }
     }
+    public partial class AmbiguousActionException : System.InvalidOperationException
+    {
+        protected AmbiguousActionException(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
+        public AmbiguousActionException(string message) { }
+    }
     public partial class CompatibilitySwitch<TValue> : Microsoft.AspNetCore.Mvc.Infrastructure.ICompatibilitySwitch where TValue : struct
     {
         public CompatibilitySwitch(string name) { }
diff --git a/src/Mvc/Mvc.Core/src/ActionConstraints/HttpMethodActionConstraint.cs b/src/Mvc/Mvc.Core/src/ActionConstraints/HttpMethodActionConstraint.cs
index 4385e734e5..a8a462da7e 100644
--- a/src/Mvc/Mvc.Core/src/ActionConstraints/HttpMethodActionConstraint.cs
+++ b/src/Mvc/Mvc.Core/src/ActionConstraints/HttpMethodActionConstraint.cs
@@ -4,16 +4,32 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using Microsoft.AspNetCore.Routing;
 
 namespace Microsoft.AspNetCore.Mvc.ActionConstraints
 {
-    internal class HttpMethodActionConstraint : IActionConstraint
+    /// <summary>
+    /// The implementation of <see cref="IActionResult" /> used to enforce
+    /// HTTP method filtering when MVC is used with legacy <see cref="IRouter" />
+    /// support. The <see cref="HttpMethodActionConstraint" /> can be used to determine
+    /// the set of HTTP methods supported by an action.
+    /// </summary>
+    public class HttpMethodActionConstraint : IActionConstraint
     {
+        /// <summary>
+        /// The <see cref="IActionConstraint.Order" /> value used by <see cref="HttpMethodActionConstraint" />.
+        /// </summary>
         public static readonly int HttpMethodConstraintOrder = 100;
 
         private readonly IReadOnlyList<string> _httpMethods;
 
-        // Empty collection means any method will be accepted.
+        /// <summary>
+        /// Creates a new instance of <see cref="HttpMethodActionConstraint" />.
+        /// </summary>
+        /// <param name="httpMethods">
+        /// The list of HTTP methods to allow. Providing an empty list will allow
+        /// any HTTP method.
+        /// </param>
         public HttpMethodActionConstraint(IEnumerable<string> httpMethods)
         {
             if (httpMethods == null)
@@ -36,10 +52,15 @@ namespace Microsoft.AspNetCore.Mvc.ActionConstraints
             _httpMethods = new ReadOnlyCollection<string>(methods);
         }
 
+        /// <summary>
+        /// Gets the list of allowed HTTP methods. Will return an empty list if all HTTP methods are allowed.
+        /// </summary>
         public IEnumerable<string> HttpMethods => _httpMethods;
 
+        /// <inheritdoc />
         public int Order => HttpMethodConstraintOrder;
 
+        /// <inheritdoc />
         public virtual bool Accept(ActionConstraintContext context)
         {
             if (context == null)
diff --git a/src/Mvc/Mvc.Core/src/Infrastructure/AmbiguousActionException.cs b/src/Mvc/Mvc.Core/src/Infrastructure/AmbiguousActionException.cs
index afe28c0209..145b5713e0 100644
--- a/src/Mvc/Mvc.Core/src/Infrastructure/AmbiguousActionException.cs
+++ b/src/Mvc/Mvc.Core/src/Infrastructure/AmbiguousActionException.cs
@@ -10,13 +10,22 @@ namespace Microsoft.AspNetCore.Mvc.Infrastructure
     /// An exception which indicates multiple matches in action selection.
     /// </summary>
     [Serializable]
-    internal class AmbiguousActionException : InvalidOperationException
+    public class AmbiguousActionException : InvalidOperationException
     {
+        /// <summary>
+        /// Creates a new instance of <see cref="AmbiguousActionException" />.
+        /// </summary>
+        /// <param name="message">The exception message.</param>
         public AmbiguousActionException(string message)
             : base(message)
         {
         }
 
+        /// <summary>
+        /// Framework infrastructure. Do not call directly.
+        /// </summary>
+        /// <param name="info"></param>
+        /// <param name="context"></param>
         protected AmbiguousActionException(SerializationInfo info, StreamingContext context)
             : base(info, context)
         {