TIP: Configuring Notepad++ to use the XML lexer on any file type with XML content

Say you've inherited a build infrastructure which you must maintain which has many files with different file extensions but the file format for all files is XML. Some of these extensions could be legitimate .xml, .config and .xslt for example with other files having proprietary extensions such as .nant, .deploy, .dist and many more. The goal is not just to be able to double click on them to automatically open them in Notepad++ (simple), but to have Notepad++ open the file with the XML lexer so all those XML tokens come up nice and colourful for ease of reading / editing. This saves time and makes editing files much less error prone. So, how is this done? In two parts... This example has been done on 32-bit Windows XP and 64-bit Windows 7 with 32-bit Notepad++ 5.8.7 and higher.

Associating the file extensions with the Notepad++ application

First the easy part... For each distinct file extension, right click, select Open with, select Choose default program. If Notepad++ is not listed, click Browse and find the executable and select it and click Open. Ensure the Always use the selected program to open this kind of file check box is ticked. Click OK and voila! FYI: the association of an application with a file extension is stored in the Windows registry.

Associating any file extension with the Notepad++ XML lexer

Now, for the less obvious part... It took me a while to realise that you can tell Notepad++ what file extensions (both standard and proprietary) should use the XML lexer rather than than having to manually set it every time (annoying!) via the Notepad++ Languages menu. To achieve this, open Notepad++, select Settings from the menu bar and click on Style configurator... Under Language, select XML. Under this list is a text box called Default ext which lists what extensions currently use the XML lexer. Opposite that text box is another called Custom ext. Add your new extensions, such as .config, .nant, .deploy or .dist etc here - ensure they are space delimited excluding the dot / period so the list looks like config nant deploy dist and click OK. FYI: these changes are saved in Notepad++'s styles.xml file usually found under said programs application data location (default location is under Documents & Settings for XP and Users for Win7).

Now, whenever you double click on any .config, .xslt, .nant, .deploy or .dist file, it will be automatically opened in Notepad++ with the XML lexer. Happy days!