Options, Text Editor, File Extension
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
This Options dialog allows you to specify how all files with certain file extensions will be handled by the Visual Studio integrated development environment (IDE). For each Extension that you enter, you can select an Editing Experience. This allows you to choose the IDE editor or designer in which documents of a certain type will open. To display these options, choose Options from the Tools menu, expand the Text Editor node, and select File Extension.
When you select an option "with Encoding," a dialog will be displayed whenever you open a document of that type that allows you to select an encoding scheme for that document. This can be helpful if you are preparing versions of your project documents for use on different platforms or in different target languages.
UIElement list
Extension
Type the file extension whose Editing Experience in the IDE you wish to define.
Editor
Select the IDE editor or designer in which documents with this file extension will open. When you select an option "with ncoding," a dialog will be displayed whenever you open such a document that allows you to select an encoding scheme.
Add
Adds an entry that includes the specified Extension and Editing Experience to the Extension List.
Remove
Deletes the selected entry from the Extension List.
Extension List
Lists all extensions for which an Editing Experience has been specified.
Map extensionless files to
Select this option if you wish to specify how files without an extension will be handled by the IDE.
Extensionless file options
Provides the same list as Editor. Select the IDE editor or designer in which documents without file extensions will open.