Update & clarify /RootSuffix command-line switch description

Update the docs to remove the reference to the VSRegEx.exe tool that does not exist in recent versions of Visual Studio. Also, make it clear that running the tool is not required to create new instances and document restrictions on the instance name.

Author: CraftyCraftress

docs/extensibility/devenv-command-line-switches-for-vspackage-development.md

@@ -37,7 +37,7 @@ Visual Studio documentation describes the user-level `devenv` command-line switc
 | Command-line switch | Description |
 |---------------------| - |
 | `/ResetSkipPkgs` | Clears all skip loading options that have been added by users who want to avoid loading problematic VSPackages, then starts Visual Studio. The presence of a SkipLoading tag disables the loading of a VSPackage. Clearing the tag re-enables the loading of the VSPackage.<br /><br /> This switch takes no arguments. |
-| `/RootSuffix` | Starts Visual Studio by using an alternate location. The following command is run by the shortcut created by the Visual Studio SDK installer:<br /><br /> `devenv /RootSuffix exp`<br /><br /> In this case, `exp` identifies a location with a particular suffix (for example, `10.0Exp` instead of `10.0`). The experimental instance allows you to debug a VSPackage separately from the instance of Visual Studio that you're using to write code.<br /><br /> This switch can take any string that identifies a location that you've created by using VSRegEx.exe. For more information, see [The Experimental Instance](../extensibility/the-experimental-instance.md). |
+| `/RootSuffix` | Starts Visual Studio by using an alternate location. The following command is run by the shortcut created by the Visual Studio SDK installer:<br /><br /> `devenv /RootSuffix exp`<br /><br /> In this case, `exp` identifies a location with a particular suffix (for example, `10.0Exp` instead of `10.0`). The experimental instance allows you to debug a VSPackage separately from the instance of Visual Studio that you're using to write code.<br /><br /> This switch can take any string that either identifies a location that you've created by using [CreateExpInstance.exe](../extensibility/internals/createexpinstance-utility.md) or the name of an instance to be created. The name of the instance must be a valid file name. For more information, see [The Experimental Instance](../extensibility/the-experimental-instance.md). |
 | `/SafeMode` | Launches Visual Studio in safe mode, loading only the default IDE and services. The `/SafeMode` switch prevents all third-party VSPackages from loading when Visual Studio starts, ensuring stable execution.<br /><br /> This switch takes no arguments. |
 | `/Setup` | Forces Visual Studio to merge resource metadata that describes menus, toolbars, and command groups from all available VSPackages. You can only run this command as an administrator. <br /><br /> This switch takes no arguments. The `devenv /Setup` command is typically given as the last step of the installation process. Use of the `/Setup` switch doesn't start the IDE.|
 | `/Splash` | Shows the Visual Studio splash screen, as usual, and then shows a message box before showing the main IDE. The message box lets you study the splash screen (for example, to check for a VSPackage product icon).<br /><br /> This switch takes no arguments. |