dotnet · Rick-Anderson · Sep 24, 2019 · May 3, 2019
diff --git a/aspnetcore/includes/built-in-TH.md b/aspnetcore/includes/built-in-TH.md
@@ -20,11 +20,11 @@
 
 **[Label Tag Helper](xref:mvc/views/working-with-forms#the-label-tag-helper)**
 
-[comment]: **[LinkTagHelper](xref:mvc/views/tag-helpers/builtin-th/link-tag-helper)**
+**[LinkTagHelper](xref:mvc/views/tag-helpers/builtin-th/link-tag-helper)**
 
 [comment]: **[OptionTagHelper](xref:mvc/views/tag-helpers/builtin-th/option-tag-helper)**
 
-[comment]: **[ScriptTagHelper](xref:mvc/views/tag-helpers/builtin-th/script-tag-helper)**
+**[ScriptTagHelper](xref:mvc/views/tag-helpers/builtin-th/script-tag-helper)**
 
 **[Partial Tag Helper](xref:mvc/views/tag-helpers/builtin-th/partial-tag-helper)**
 

diff --git a/aspnetcore/includes/cdn.md b/aspnetcore/includes/cdn.md
@@ -0,0 +1,4 @@
+A CDN:
+
+* Provides several [performance advantages](/office365/enterprise/content-delivery-networks#how-do-cdns-make-services-work-faster) vs hosting the asset with the web app.
+* Should not be relied on as the only source for the asset. CDNs are not always available, therefore a reliable fallback should be used. Typically the fallback is the site hosting the web app.
diff --git a/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper.md b/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper.md
@@ -0,0 +1,63 @@
+---
+title: Link Tag Helper in ASP.NET Core
+author: rick-anderson
+ms.author: riande
+description: Discover the ASP.NET Core Link Tag Helper attributes and the role each attribute plays in extending behavior of the HTML Link tag.
+ms.custom: mvc
+ms.date: 4/
+uid: mvc/views/tag-helpers/builtin-th/link-tag-helper
+---
+# Link Tag Helper in ASP.NET Core
+
+By [Rick Anderson](https://twitter.com/RickAndMSFT)
+
+The [Link Tag Helper](xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper) generates a link to a primary or fall back CSS file. Typically the primary CSS file is on a [Content Delivery Network](/office365/enterprise/content-delivery-networks#what-exactly-is-a-cdn) (CDN).
+
+[!INCLUDE[](~/includes/cdn.md)]
+
+The Link Tag Helper allows you to specify a CDN for the CSS file and a fallback when the CDN is not available. The Link Tag Helper provides the performance advantage of a CDN with the robustness of local hosting.
+
+The following Razor markup shows the `head` element of a layout file created with the ASP.NET Core web app template:
+
+[!code-html[](link-tag-helper/sample/_Layout.cshtml?name=snippet)]
+
+The following is rendered HTML from the preceding code (in a non-Development environment):
+
+[!code-csharp[](link-tag-helper/sample/HtmlPage1.html)]
+
+In the preceding code, the Link Tag Helper generated the `<meta name="x-stylesheet-fallback-test" content="" class="sr-only" />` element and the following JavaScript which is used to verify the requested *bootstrap.min.css* file is available on the CDN. In this case, the CSS file was available so the Tag Helper generated the `<link />` element with the CDN CSS file.
+
+## Commonly used Link Tag Helper attributes
+
+See [Link Tag Helper](xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper)  for all the Link Tag Helper attributes, properties, and methods.
+
+### href
+
+Preferred address of the linked resource. The address is passed thought to the generated HTML in all cases.
+
+### asp-fallback-href
+
+The URL of a CSS stylesheet to fallback to in the case the primary URL fails.
+
+### asp-fallback-test-class
+
+The class name defined in the stylesheet to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestClass>.
+
+### asp-fallback-test-property
+
+The CSS property name to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestProperty>.
+
+### asp-fallback-test-value
+
+The CSS property value to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestValue>.
+
+### asp-fallback-test-value
+
+The CSS property value to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestValue>
+
+## Additional resources
+
+* <xref:mvc/views/tag-helpers/intro>
+* <xref:mvc/controllers/areas>
+* <xref:razor-pages/index>
+* <xref:mvc/compatibility-version>
diff --git a/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper/sample/HtmlPage1.html b/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper/sample/HtmlPage1.html
@@ -0,0 +1,23 @@
+<html>
+<head>
+    <meta charset="utf-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Home page - WebLinkTH</title>
+    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.1.3/css/bootstrap.min.css"
+          crossorigin="anonymous" integrity="sha256-eS<snip>BE=" />
+    <meta name="x-stylesheet-fallback-test" content="" class="sr-only" />
+    <script>
+        !function (a, b, c, d) {
+            var e, f = document,
+                g = f.getElementsByTagName("SCRIPT"),
+                h = g[g.length - 1].previousElementSibling,
+                i = f.defaultView && f.defaultView.getComputedStyle ? f.defaultView.getComputedStyle(h) : h.currentStyle;
+            if (i && i[a] !== b) for (e = 0; e < c.length; e++)
+                f.write('<link href="' + c[e] + '" ' + d + "/>")
+        }
+            ("position", "absolute", ["\/lib\/bootstrap\/dist\/css\/bootstrap.min.css"],
+                "rel=\u0022stylesheet\u0022 crossorigin=\u0022anonymous\u0022 integrity=\abc<snip>BE=\u0022 ");
+    </script>
+
+    <link rel="stylesheet" href="/css/site.css" />
+</head>
diff --git a/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper/sample/HtmlPage2.html b/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper/sample/HtmlPage2.html
@@ -0,0 +1,11 @@
+<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"
+        crossorigin="anonymous"
+        integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=">
+</script>
+<script>  (window.jQuery || document.write(
+        "\u003Cscript src=\u0022\/lib\/jquery\/dist\/jquery.min.js\u0022 " +
+        "crossorigin =\u0022anonymous\u0022 integrity =\u0022sha256 - " +
+        "FgpCb\/KJQ32o\/NM<snip>u8=\u0022\u003E\u003C\/script\u003E"));
+</script>
+
+
diff --git a/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper/sample/_Layout.cshtml b/aspnetcore/mvc/views/tag-helpers/built-in/link-tag-helper/sample/_Layout.cshtml
@@ -0,0 +1,83 @@
+ <!-- <snippet> -->
+<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>@ViewData["Title"] - WebLinkTH</title>
+
+    <environment include="Development">
+        <link rel="stylesheet" href="~/lib/bootstrap/dist/css/bootstrap.css" />
+    </environment>
+    <environment exclude="Development">
+        <link rel="stylesheet" 
+              href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.1.3/css/bootstrap.min.css"
+              asp-fallback-href="~/lib/bootstrap/dist/css/bootstrap.min.css"
+              asp-fallback-test-class="sr-only" asp-fallback-test-property="position" 
+              asp-fallback-test-value="absolute"
+              crossorigin="anonymous"
+              integrity="sha256-eSi1q2PG6J7g7ib17yAaWMcrr5GrtohYChqibrV7PBE=" />
+    </environment>
+    <link rel="stylesheet" href="~/css/site.css" />
+</head>
+<!-- </snippet> -->
+<body>
+    <header>
+        <nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
+            <div class="container">
+                <a class="navbar-brand" asp-area="" asp-page="/Index">WebLinkTH</a>
+                <button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-collapse" aria-controls="navbarSupportedContent"
+                        aria-expanded="false" aria-label="Toggle navigation">
+                    <span class="navbar-toggler-icon"></span>
+                </button>
+                <div class="navbar-collapse collapse d-sm-inline-flex flex-sm-row-reverse">
+                    <ul class="navbar-nav flex-grow-1">
+                        <li class="nav-item">
+                            <a class="nav-link text-dark" asp-area="" asp-page="/Index">Home</a>
+                        </li>
+                        <li class="nav-item">
+                            <a class="nav-link text-dark" asp-area="" asp-page="/Privacy">Privacy</a>
+                        </li>
+                    </ul>
+                </div>
+            </div>
+        </nav>
+    </header>
+    <div class="container">
+        <partial name="_CookieConsentPartial" />
+        <main role="main" class="pb-3">
+            @RenderBody()
+        </main>
+    </div>
+
+    <footer class="border-top footer text-muted">
+        <div class="container">
+            &copy; 2019 - WebLinkTH - <a asp-area="" asp-page="/Privacy">Privacy</a>
+        </div>
+    </footer>
+
+    <environment include="Development">
+        <script src="~/lib/jquery/dist/jquery.js"></script>
+        <script src="~/lib/bootstrap/dist/js/bootstrap.bundle.js"></script>
+    </environment>
+    <environment exclude="Development">
+        <!-- <snippet2> -->
+        <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"
+                asp-fallback-src="~/lib/jquery/dist/jquery.min.js"
+                asp-fallback-test="window.jQuery"
+                crossorigin="anonymous"
+                integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=">
+        </script>
+        <!-- </snippet2> -->
+        <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.1.3/js/bootstrap.bundle.min.js"
+                asp-fallback-src="~/lib/bootstrap/dist/js/bootstrap.bundle.min.js"
+                asp-fallback-test="window.jQuery && window.jQuery.fn && window.jQuery.fn.modal"
+                crossorigin="anonymous"
+                integrity="sha256-E/V4cWE4qvAeO5MOhjtGtqDzPndRO1LBk8lJ/PR7CA4=">
+        </script>
+    </environment>
+    <script src="~/js/site.js" asp-append-version="true"></script>
+
+    @RenderSection("Scripts", required: false)
+</body>
+</html>
diff --git a/aspnetcore/mvc/views/tag-helpers/built-in/script-tag-helper.md b/aspnetcore/mvc/views/tag-helpers/built-in/script-tag-helper.md
@@ -0,0 +1,63 @@
+---
+title: Script Tag Helper in ASP.NET Core
+author: rick-anderson
+ms.author: riande
+description: Discover the ASP.NET Core Script Tag Helper attributes and the role each attribute plays in extending behavior of the HTML Script tag.
+ms.custom: mvc
+ms.date: 12/18/2018
+uid: mvc/views/tag-helpers/builtin-th/script-tag-helper
+---
+# Script Tag Helper in ASP.NET Core
+
+By [Rick Anderson](https://twitter.com/RickAndMSFT)
+
+The [Script Tag Helper](xref:Microsoft.AspNetCore.Mvc.TagHelpers.ScriptTagHelper) generates a link to a primary or fall back script file. Typically the primary script file is on a [Content Delivery Network](/office365/enterprise/content-delivery-networks#what-exactly-is-a-cdn) (CDN).
+
+[!INCLUDE[](~/includes/cdn.md)]
+
+The Script Tag Helper allows you to specify a CDN for the script file and a fallback when the CDN is not available. The Script Tag Helper provides the performance advantage of a CDN with the robustness of local hosting.
+
+The following Razor markup shows the `script` element of a layout file created with the ASP.NET Core web app template:
+
+[!code-html[](link-tag-helper/sample/_Layout.cshtml?name=snippet2)]
+
+The following is similar to the rendered HTML from the preceding code (in a non-Development environment):
+
+[!code-csharp[](link-tag-helper/sample/HtmlPage2.html)]
+
+In the preceding code, the Script Tag Helper generated the second script ( `<script>  (window.jQuery || document.write(`) element, which tests for `window.jQuery`. If `window.jQuery` is not found, `document.write(` runs and creates a script 
+
+## Commonly used Script Tag Helper attributes
+
+See [Script Tag Helper](xref:Microsoft.AspNetCore.Mvc.TagHelpers.ScriptTagHelper) for all the Script Tag Helper attributes, properties, and methods.
+
+### href
+
+Preferred address of the linked resource. The address is passed thought to the generated HTML in all cases.
+
+### asp-fallback-href
+
+The URL of a CSS stylesheet to fallback to in the case the primary URL fails.
+
+### asp-fallback-test-class
+
+The class name defined in the stylesheet to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestClass>.
+
+### asp-fallback-test-property
+
+The CSS property name to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestProperty>.
+
+### asp-fallback-test-value
+
+The CSS property value to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestValue>.
+
+### asp-fallback-test-value
+
+The CSS property value to use for the fallback test. For more information, see <xref:Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper.FallbackTestValue>
+
+## Additional resources
+
+* <xref:mvc/views/tag-helpers/intro>
+* <xref:mvc/controllers/areas>
+* <xref:razor-pages/index>
+* <xref:mvc/compatibility-version>