You might find it useful, to open files of your .NET-solution directly from Windows Explorer without launching Visual Studio. For that purpose, Notepad++ is a perfect choice.
Besides other goodness, Notepad++ provides syntax highlighting. But for that to work properly, Notepad++ must know the language of the file’s content. Especially there are several files in an XML format that do have a file extension other than xml. The best example may be project files (*.csproj, *.vbproj). Other examples are the extensions xaml, config, wsdl, etc. For those files, it may be cumbersome to tell Notepad++ after opening the file, what language the file content is.
Fortunately, the mappings of file extensions to languages can be configured in the file langs.xml, found in %AppData%\Notepad++. That file has a Language-element for each language along with a ext attribute. That ext-attribute lists all file extensions that Notepad++ recognizes for the respective language.
Mine looks like this:
After relaunching Notepad++, it automatically chooses the language of a newly opened file according to that mapping.
Tip: For a selection of file editors (including Notepad++), see this post.