I have Juniper_JunOS.xml file and I want to add this language to notepad++ languages. How can I do this? I am using windows vista
I guess you found that XML from the official list of User Defined Languages.
If you scroll down at that page, you will notice that there's a How to install user defined language files
section, where it states: To add syntax colouring from one of these, the simplest way is to open the User Defined Language panel, click "Import" and navigate to the desired file.
So, in Notepad++ v6.5.1. (latest version), go to menu Language
> Define your language...
and then press Import
button and select your XML file.