Addressed code review comments.

src/Microsoft.AspNet.Mvc.TagHelpers/OptionTagHelper.cs

@@ -55,7 +55,7 @@ public override int Order
         /// <inheritdoc />
         /// <remarks>
         /// Does nothing unless <see cref="TagHelperContext.Items"/> contains a
-        /// <see cref="SelectTagHelper.SelectedValuesFormDataKey"/> entry and that entry is a non-empty
+        /// <see cref="SelectTagHelper"/> <see cref="Type"/> entry and that entry is a non-empty
         /// <see cref="ICollection{string}"/> instance. Also does nothing if the associated &lt;option&gt; is already
         /// selected.
         /// </remarks>
@@ -82,9 +82,7 @@ public override async Task ProcessAsync(TagHelperContext context, TagHelperOutpu
             {
                 // Is this <option/> element a child of a <select/> element the SelectTagHelper targeted?
                 object formDataEntry;
-                context.Items.TryGetValue(
-                    SelectTagHelper.SelectedValuesFormDataKey,
-                    out formDataEntry);
+                context.Items.TryGetValue(typeof(SelectTagHelper), out formDataEntry);
 
                 // ... And did the SelectTagHelper determine any selected values?
                 var selectedValues = formDataEntry as ICollection<string>;

src/Microsoft.AspNet.Mvc.TagHelpers/SelectTagHelper.cs

@@ -22,16 +22,6 @@ public class SelectTagHelper : TagHelper
         private const string ForAttributeName = "asp-for";
         private const string ItemsAttributeName = "asp-items";
 
-        /// <summary>
-        /// Key used for selected values in <see cref="TagHelperContext.Items"/>.
-        /// </summary>
-        /// <remarks>
-        /// Value for this dictionary entry will either be <c>null</c> (indicating no <see cref="SelectTagHelper"/> has
-        /// executed within this &lt;form/&gt;) or an <see cref="ICollection{string}"/> instance. Elements of the
-        /// collection are based on current <see cref="ViewDataDictionary.Model"/>.
-        /// </remarks>
-        public static readonly string SelectedValuesFormDataKey = nameof(SelectTagHelper) + "-SelectedValues";
-
         /// <summary>
         /// Creates a new <see cref="SelectTagHelper"/>.
         /// </summary>
@@ -131,7 +121,7 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
 
             // Whether or not (not being highly unlikely) we generate anything, could update contained <option/>
             // elements. Provide selected values for <option/> tag helpers. They'll run next.
-            context.Items[SelectedValuesFormDataKey] = currentValues;
+            context.Items[typeof(SelectTagHelper)] = currentValues;
         }
     }
 }

test/Microsoft.AspNet.Mvc.TagHelpers.Test/OptionTagHelperTest.cs

@@ -420,7 +420,7 @@ public async Task ProcessAsync_GeneratesExpectedOutput(
                 model: null,
                 htmlGenerator: htmlGenerator,
                 metadataProvider: metadataProvider);
-            tagHelperContext.Items[SelectTagHelper.SelectedValuesFormDataKey] = selectedValues;
+            tagHelperContext.Items[typeof(SelectTagHelper)] = selectedValues;
             var tagHelper = new OptionTagHelper(htmlGenerator)
             {
                 Value = value,
@@ -491,7 +491,7 @@ public async Task ProcessAsync_DoesNotUseGenerator_IfSelectedNullOrNoSelectedVal
                 model: null,
                 htmlGenerator: htmlGenerator,
                 metadataProvider: metadataProvider);
-            tagHelperContext.Items[SelectTagHelper.SelectedValuesFormDataKey] = selectedValues;
+            tagHelperContext.Items[typeof(SelectTagHelper)] = selectedValues;
             var tagHelper = new OptionTagHelper(htmlGenerator)
             {
                 Value = value,

test/Microsoft.AspNet.Mvc.TagHelpers.Test/SelectTagHelperTest.cs

@@ -247,7 +247,7 @@ public async Task ProcessAsync_GeneratesExpectedOutput(
 
             Assert.Single(
                 tagHelperContext.Items,
-                entry => (string)entry.Key == SelectTagHelper.SelectedValuesFormDataKey);
+                entry => (Type)entry.Key == typeof(SelectTagHelper));
         }
 
         [Theory]
@@ -344,7 +344,7 @@ public async Task ProcessAsync_WithItems_GeneratesExpectedOutput_DoesNotChangeSe
 
             Assert.Single(
                 tagHelperContext.Items,
-                entry => (string)entry.Key == SelectTagHelper.SelectedValuesFormDataKey);
+                entry => (Type)entry.Key == typeof(SelectTagHelper));
 
             Assert.Equal(savedDisabled, items.Select(item => item.Disabled));
             Assert.Equal(savedGroup, items.Select(item => item.Group));
@@ -448,7 +448,7 @@ public async Task ProcessAsyncInTemplate_WithItems_GeneratesExpectedOutput_DoesN
 
             Assert.Single(
                 tagHelperContext.Items,
-                entry => (string)entry.Key == SelectTagHelper.SelectedValuesFormDataKey);
+                entry => (Type)entry.Key == typeof(SelectTagHelper));
 
             Assert.Equal(savedDisabled, items.Select(item => item.Disabled));
             Assert.Equal(savedGroup, items.Select(item => item.Group));
@@ -540,7 +540,7 @@ public async Task ProcessAsync_CallsGeneratorWithExpectedValues_ItemsAndAttribut
 
             var keyValuePair = Assert.Single(
                 tagHelperContext.Items,
-                entry => (string)entry.Key == SelectTagHelper.SelectedValuesFormDataKey);
+                entry => (Type)entry.Key == typeof(SelectTagHelper));
             Assert.Same(currentValues, keyValuePair.Value);
         }
 
@@ -613,7 +613,7 @@ public async Task TagHelper_CallsGeneratorWithExpectedValues_RealModelType(
 
             var keyValuePair = Assert.Single(
                 tagHelperContext.Items,
-                entry => (string)entry.Key == SelectTagHelper.SelectedValuesFormDataKey);
+                entry => (Type)entry.Key == typeof(SelectTagHelper));
             Assert.Same(currentValues, keyValuePair.Value);
         }