diff --git a/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/DefaultTagHelperContent.cs b/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/DefaultTagHelperContent.cs
index 630d19e9ab..4c93aa29b1 100644
--- a/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/DefaultTagHelperContent.cs
+++ b/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/DefaultTagHelperContent.cs
@@ -133,137 +133,6 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             return this;
         }
 
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(string format, object arg0)
-        {
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(format, arg0));
-            return this;
-        }
-
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(string format, object arg0, object arg1)
-        {
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(format, arg0, arg1));
-            return this;
-        }
-
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(string format, object arg0, object arg1, object arg2)
-        {
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(format, arg0, arg1, arg2));
-            return this;
-        }
-
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(string format, params object[] args)
-        {
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(format, args));
-            return this;
-        }
-
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(
-            IFormatProvider provider,
-            string format,
-            object arg0)
-        {
-            if (provider == null)
-            {
-                throw new ArgumentNullException(nameof(provider));
-            }
-
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(provider, format, arg0));
-            return this;
-        }
-
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(
-            IFormatProvider provider,
-            string format,
-            object arg0,
-            object arg1)
-        {
-            if (provider == null)
-            {
-                throw new ArgumentNullException(nameof(provider));
-            }
-
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(provider, format, arg0, arg1));
-            return this;
-        }
-
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(
-            IFormatProvider provider,
-            string format,
-            object arg0,
-            object arg1,
-            object arg2)
-        {
-            if (provider == null)
-            {
-                throw new ArgumentNullException(nameof(provider));
-            }
-
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(provider, format, arg0, arg1, arg2));
-            return this;
-        }
-
-        /// <inheritdoc />
-        public override TagHelperContent AppendFormat(
-            IFormatProvider provider,
-            string format,
-            params object[] args)
-        {
-            if (provider == null)
-            {
-                throw new ArgumentNullException(nameof(provider));
-            }
-
-            if (format == null)
-            {
-                throw new ArgumentNullException(nameof(format));
-            }
-
-            Buffer.Append(string.Format(provider, format, args));
-            return this;
-        }
-
         /// <inheritdoc />
         public override TagHelperContent Append(IHtmlContent htmlContent)
         {
diff --git a/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperContent.cs b/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperContent.cs
index ee274b6a6a..4f86f4bd99 100644
--- a/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperContent.cs
+++ b/src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperContent.cs
@@ -11,7 +11,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
     /// <summary>
     /// Abstract class used to buffer content returned by <see cref="ITagHelper"/>s.
     /// </summary>
-    public abstract class TagHelperContent : IHtmlContent
+    public abstract class TagHelperContent : IHtmlContentBuilder
     {
         /// <summary>
         /// Gets a value indicating whether the content was modifed.
@@ -31,24 +31,39 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// <summary>
         /// Sets the content.
         /// </summary>
-        /// <param name="value">The <see cref="string"/> that replaces the content.</param>
+        /// <param name="htmlContent">The <see cref="IHtmlContent"/> that replaces the content.</param>
         /// <returns>A reference to this instance after the set operation has completed.</returns>
-        public TagHelperContent SetContent(string value)
+        public TagHelperContent SetContent(IHtmlContent htmlContent)
         {
-            Clear();
-            Append(value);
+            HtmlContentBuilderExtensions.SetContent(this, htmlContent);
             return this;
         }
 
         /// <summary>
         /// Sets the content.
         /// </summary>
-        /// <param name="htmlContent">The <see cref="IHtmlContent"/> that replaces the content.</param>
+        /// <param name="unencoded">
+        /// The <see cref="string"/> that replaces the content. The value is assume to be unencoded
+        /// as-provided and will be HTML encoded before being written.
+        /// </param>
         /// <returns>A reference to this instance after the set operation has completed.</returns>
-        public TagHelperContent SetContent(IHtmlContent htmlContent)
+        public TagHelperContent SetContent(string unencoded)
         {
-            Clear();
-            Append(htmlContent);
+            HtmlContentBuilderExtensions.SetContent(this, unencoded);
+            return this;
+        }
+
+        /// <summary>
+        /// Sets the content.
+        /// </summary>
+        /// <param name="encoded">
+        /// The <see cref="string"/> that replaces the content. The value is assume to be HTML encoded
+        /// as-provided and no further encoding will be performed.
+        /// </param>
+        /// <returns>A reference to this instance after the set operation has completed.</returns>
+        public TagHelperContent SetContentEncoded(string encoded)
+        {
+            HtmlContentBuilderExtensions.SetContentEncoded(this, encoded);
             return this;
         }
 
@@ -59,6 +74,13 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// <returns>A reference to this instance after the append operation has completed.</returns>
         public abstract TagHelperContent Append(string value);
 
+        /// <summary>
+        /// Appends <paramref name="htmlContent"/> to the existing content.
+        /// </summary>
+        /// <param name="htmlContent">The <see cref="IHtmlContent"/> to be appended.</param>
+        /// <returns>A reference to this instance after the append operation has completed.</returns>
+        public abstract TagHelperContent Append(IHtmlContent htmlContent);
+
         /// <summary>
         /// Appends <paramref name="value"/> to the existing content. <paramref name="value"/> is assumed
         /// to be an HTML encoded <see cref="string"/> and no further encoding will be performed.
@@ -69,46 +91,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 
         /// <summary>
         /// Appends the specified <paramref name="format"/> to the existing content after
-        /// replacing the format item with the <see cref="string"/> representation of the
-        /// <paramref name="arg0"/>.
-        /// </summary>
-        /// <param name="format">
-        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
-        /// </param>
-        /// <param name="arg0">The object to format.</param>
-        /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(string format, object arg0);
-
-        /// <summary>
-        /// Appends the specified <paramref name="format"/> to the existing content after
-        /// replacing each format item with the <see cref="string"/> representation of the
-        /// <paramref name="arg0"/> and <paramref name="arg1"/>.
-        /// </summary>
-        /// <param name="format">
-        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
-        /// </param>
-        /// <param name="arg0">The object to format.</param>
-        /// <param name="arg1">The object to format.</param>
-        /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(string format, object arg0, object arg1);
-
-        /// <summary>
-        /// Appends the specified <paramref name="format"/> to the existing content after
-        /// replacing each format item with the <see cref="string"/> representation of the
-        /// <paramref name="arg0"/>, <paramref name="arg1"/> and <paramref name="arg2"/>.
-        /// </summary>
-        /// <param name="format">
-        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
-        /// </param>
-        /// <param name="arg0">The object to format.</param>
-        /// <param name="arg1">The object to format.</param>
-        /// <param name="arg2">The object to format.</param>
-        /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(string format, object arg0, object arg1, object arg2);
-
-        /// <summary>
-        /// Appends the specified <paramref name="format"/> to the existing content after
-        /// replacing each format item with the <see cref="string"/> representation of the
+        /// replacing each format item with the HTML encoded <see cref="string"/> representation of the
         /// corresponding item in the <paramref name="args"/> array.
         /// </summary>
         /// <param name="format">
@@ -116,63 +99,15 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// </param>
         /// <param name="args">The object array to format.</param>
         /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(string format, params object[] args);
+        public TagHelperContent AppendFormat(string format, params object[] args)
+        {
+            HtmlContentBuilderExtensions.AppendFormat(this, null, format, args);
+            return this;
+        }
 
         /// <summary>
         /// Appends the specified <paramref name="format"/> to the existing content with information from the
-        /// <paramref name="provider"/> after replacing the format item with the <see cref="string"/>
-        /// representation of the corresponding item in <paramref name="arg0"/>.
-        /// </summary>
-        /// <param name="provider">An object that supplies culture-specific formatting information.</param>
-        /// <param name="format">
-        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
-        /// </param>
-        /// <param name="arg0">The object to format.</param>
-        /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(IFormatProvider provider, string format, object arg0);
-
-        /// <summary>
-        /// Appends the specified <paramref name="format"/> to the existing content with information from the
-        /// <paramref name="provider"/> after replacing each format item with the <see cref="string"/>
-        /// representation of the corresponding item in <paramref name="arg0"/> and <paramref name="arg1"/>.
-        /// </summary>
-        /// <param name="provider">An object that supplies culture-specific formatting information.</param>
-        /// <param name="format">
-        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
-        /// </param>
-        /// <param name="arg0">The object to format.</param>
-        /// <param name="arg1">The object to format.</param>
-        /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(
-            IFormatProvider provider,
-            string format,
-            object arg0,
-            object arg1);
-
-        /// <summary>
-        /// Appends the specified <paramref name="format"/> to the existing content with information from the
-        /// <paramref name="provider"/> after replacing each format item with the <see cref="string"/>
-        /// representation of the corresponding item in <paramref name="arg0"/>, <paramref name="arg1"/>
-        /// and <paramref name="arg2"/>.
-        /// </summary>
-        /// <param name="provider">An object that supplies culture-specific formatting information.</param>
-        /// <param name="format">
-        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
-        /// </param>
-        /// <param name="arg0">The object to format.</param>
-        /// <param name="arg1">The object to format.</param>
-        /// <param name="arg2">The object to format.</param>
-        /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(
-            IFormatProvider provider,
-            string format,
-            object arg0,
-            object arg1,
-            object arg2);
-
-        /// <summary>
-        /// Appends the specified <paramref name="format"/> to the existing content with information from the
-        /// <paramref name="provider"/> after replacing each format item with the <see cref="string"/>
+        /// <paramref name="provider"/> after replacing each format item with the HTML encoded <see cref="string"/>
         /// representation of the corresponding item in the <paramref name="args"/> array.
         /// </summary>
         /// <param name="provider">An object that supplies culture-specific formatting information.</param>
@@ -181,14 +116,11 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// </param>
         /// <param name="args">The object array to format.</param>
         /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent AppendFormat(IFormatProvider provider, string format, params object[] args);
-
-        /// <summary>
-        /// Appends <paramref name="htmlContent"/> to the existing content.
-        /// </summary>
-        /// <param name="htmlContent">The <see cref="IHtmlContent"/> to be appended.</param>
-        /// <returns>A reference to this instance after the append operation has completed.</returns>
-        public abstract TagHelperContent Append(IHtmlContent htmlContent);
+        public TagHelperContent AppendFormat(IFormatProvider provider, string format, params object[] args)
+        {
+            HtmlContentBuilderExtensions.AppendFormat(this, provider, format, args);
+            return this;
+        }
 
         /// <summary>
         /// Clears the content.
@@ -211,5 +143,29 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 
         /// <inheritdoc />
         public abstract void WriteTo(TextWriter writer, IHtmlEncoder encoder);
+
+        /// <inheritdoc />
+        IHtmlContentBuilder IHtmlContentBuilder.Append(IHtmlContent content)
+        {
+            return Append(content);
+        }
+
+        /// <inheritdoc />
+        IHtmlContentBuilder IHtmlContentBuilder.Append(string unencoded)
+        {
+            return Append(unencoded);
+        }
+
+        /// <inheritdoc />
+        IHtmlContentBuilder IHtmlContentBuilder.AppendEncoded(string encoded)
+        {
+            return AppendEncoded(encoded);
+        }
+
+        /// <inheritdoc />
+        IHtmlContentBuilder IHtmlContentBuilder.Clear()
+        {
+            return Clear();
+        }
     }
 }
\ No newline at end of file
diff --git a/test/Microsoft.AspNet.Razor.Runtime.Test/TagHelpers/DefaultTagHelperContentTest.cs b/test/Microsoft.AspNet.Razor.Runtime.Test/TagHelpers/DefaultTagHelperContentTest.cs
index 30e2f074fa..bdf2a1f00d 100644
--- a/test/Microsoft.AspNet.Razor.Runtime.Test/TagHelpers/DefaultTagHelperContentTest.cs
+++ b/test/Microsoft.AspNet.Razor.Runtime.Test/TagHelpers/DefaultTagHelperContentTest.cs
@@ -88,7 +88,6 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             Assert.Equal(expected, tagHelperContent.GetContent(new CommonTestEncoder()));
         }
 
-        // Overload with args array is called.
         [Fact]
         public void CanAppendFormatContent()
         {
@@ -100,84 +99,10 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 
             // Assert
             Assert.Equal(
-                "HtmlEncode[[First Second Third Fourth!]]",
+                "HtmlEncode[[First]] HtmlEncode[[Second]] HtmlEncode[[Third]] HtmlEncode[[Fourth]]!",
                 tagHelperContent.GetContent(new CommonTestEncoder()));
         }
-
-        [Fact]
-        public void CanAppendFormatContent_With1Argument()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat("0x{0, -5:X} - hex equivalent for 50.", 50);
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[0x32    - hex equivalent for 50.]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        public void CanAppendFormatContent_With2Arguments()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat("0x{0, -5:X} - hex equivalent for {1}.", 50, 50);
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[0x32    - hex equivalent for 50.]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        public void CanAppendFormatContent_With3Arguments()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat("0x{0, -5:X} - {1} equivalent for {2}.", 50, "hex", 50);
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[0x32    - hex equivalent for 50.]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        public void CanAppendFormat_WithAlignmentComponent()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat("{0, -10} World!", "Hello");
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[Hello      World!]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        public void CanAppendFormat_WithFormatStringComponent()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat("0x{0:X}", 50);
-
-            // Assert
-            Assert.Equal("HtmlEncode[[0x32]]", tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        // Overload with args array is called.
+        
         [Fact]
         public void CanAppendFormat_WithCulture()
         {
@@ -187,7 +112,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             // Act
             tagHelperContent.AppendFormat(
                 CultureInfo.InvariantCulture,
-                "Numbers in InvariantCulture - {0, -5:N} {1} {2} {3}!",
+                "Numbers in InvariantCulture - {0:N} {1} {2} {3}!",
                 1.1,
                 2.98,
                 145.82,
@@ -195,107 +120,19 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 
             // Assert
             Assert.Equal(
-                "HtmlEncode[[Numbers in InvariantCulture - 1.10  2.98 145.82 32.86!]]",
+                "Numbers in InvariantCulture - HtmlEncode[[1.10]] HtmlEncode[[2.98]] " +
+                    "HtmlEncode[[145.82]] HtmlEncode[[32.86]]!",
                 tagHelperContent.GetContent(new CommonTestEncoder()));
         }
 
         [Fact]
-        public void CanAppendFormat_WithCulture_1Argument()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat(
-                CultureInfo.InvariantCulture,
-                "Numbers in InvariantCulture - {0, -5:N}!",
-                1.1);
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[Numbers in InvariantCulture - 1.10 !]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        public void CanAppendFormat_WithCulture_2Arguments()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat(
-                CultureInfo.InvariantCulture,
-                "Numbers in InvariantCulture - {0, -5:N} {1}!",
-                1.1,
-                2.98);
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[Numbers in InvariantCulture - 1.10  2.98!]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        public void CanAppendFormat_WithCulture_3Arguments()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat(
-                CultureInfo.InvariantCulture,
-                "Numbers in InvariantCulture - {0, -5:N} {1} {2}!",
-                1.1,
-                2.98,
-                3.12);
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[Numbers in InvariantCulture - 1.10  2.98 3.12!]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        public void CanAppendFormat_WithDifferentCulture()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-            var culture = new CultureInfo("fr-FR");
-
-            // Act
-            tagHelperContent.AppendFormat(culture, "{0} in french!", 1.21);
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[1,21 in french!]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact]
-        [ReplaceCulture]
-        public void CanAppendFormat_WithDifferentCurrentCulture()
-        {
-            // Arrange
-            var tagHelperContent = new DefaultTagHelperContent();
-
-            // Act
-            tagHelperContent.AppendFormat(CultureInfo.CurrentCulture, "{0:D}", DateTime.Parse("01/02/2015"));
-
-            // Assert
-            Assert.Equal(
-                "HtmlEncode[[01 February 2015]]",
-                tagHelperContent.GetContent(new CommonTestEncoder()));
-        }
-
-        [Fact(Skip = "Blocked by #526")]
         public void CanAppendDefaultTagHelperContent()
         {
             // Arrange
             var tagHelperContent = new DefaultTagHelperContent();
             var helloWorldContent = new DefaultTagHelperContent();
             helloWorldContent.SetContent("HelloWorld");
-            var expected = "HtmlEncode[[Content was HelloWorld]]";
+            var expected = "Content was HtmlEncode[[HelloWorld]]";
 
             // Act
             tagHelperContent.AppendFormat("Content was {0}", helloWorldContent);
@@ -549,7 +386,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         {
             // Arrange
             var tagHelperContent = new DefaultTagHelperContent();
-            var expected = "HtmlEncode[[First ]]HtmlEncode[[Second Third]]";
+            var expected = "HtmlEncode[[First ]]HtmlEncode[[Second]] Third";
 
             // Act
             tagHelperContent.SetContent("First ").AppendFormat("{0} Third", "Second");
@@ -563,7 +400,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         {
             // Arrange
             var tagHelperContent = new DefaultTagHelperContent();
-            var expected = "HtmlEncode[[First ]]HtmlEncode[[Second Third ]]HtmlEncode[[Fourth]]";
+            var expected = "HtmlEncode[[First ]]HtmlEncode[[Second]] Third HtmlEncode[[Fourth]]";
 
             // Act
             tagHelperContent