explain ~ (dotnet#9121)

* explain ~

* Minor tweaks

* Minor tweak

* react to feedback

* Update index.md

* Update static-files.md

* react to feedback

Author: Rick Anderson

aspnetcore/fundamentals/index.md

@@ -69,9 +69,11 @@ For more information, see <xref:fundamentals/startup>.
 
 The content root is the base path to any content used by the app, such as [Razor Pages](xref:razor-pages/index), MVC views, and static assets. By default, the content root is the same location as the app base path for the executable hosting the app.
 
-## Web root
+## Web root (webroot)
 
-The web root of an app is the directory in the project containing public, static resources, such as CSS, JavaScript, and image files.
+The webroot of an app is the directory in the project containing public, static resources, such as CSS, JavaScript, and image files. By default, *wwwroot* is the webroot.
+
+For Razor (*.cshtml*) files, the tilde-slash  `~/` points to the webroot. Paths beginning with `~/` are referred to as virtual paths.
 
 ## Dependency injection (services)
 

aspnetcore/fundamentals/static-files.md

@@ -4,7 +4,7 @@ author: rick-anderson
 description: Learn how to serve and secure static files and configure static file hosting middleware behaviors in an ASP.NET Core web app.
 ms.author: riande
 ms.custom: mvc
-ms.date: 01/18/2018
+ms.date: 10/18/2018
 uid: fundamentals/static-files
 ---
 # Static files in ASP.NET Core
@@ -66,6 +66,8 @@ The parameterless `UseStaticFiles` method overload marks the files in web root a
 
 [!code-cshtml[](static-files/samples/1x/Views/Home/Index.cshtml?name=snippet_static_file_wwwroot)]
 
+In the preceding code, the tilde character `~/` points to webroot. For more information, see [Web root](xref:fundamentals/index#web-root).
+
 ### Serve files outside of web root
 
 Consider a directory hierarchy in which the static files to be served reside outside of the web root: