XML ( Extensible Markup Language ) is a markup language which main role is to define a set of rules for encoding documents in a format that is readable for humans and machines. Part of the reason why it’s become so popular is because it’s internationally accepted, and part of the reason for that is that it works with all types of software. It’s also not difficult to write XML code. It doesn’t look too dissimilar from HTML, although of course, there are differences. HTML is predefined, it has a fixed format, but if you want to use XML then you need to set your own tags (that’s where the “extensible” comes from). This aspect of it makes XML flexible. You can do a lot with it, including (if you’re feeling ambitious) writing your own language.
It may look like HTML, but that doesn’t mean that XML is meant to replace it. They do work well together though. As you might guess, XHTML markup language very much draws on XML. The XML language family is large and flexible, and it plays a leading role in web development. So, what is and XML file? It’s a text-based format that can be opened and edited with simple programs like notepad or textpad. If you see .xml after a filename then you know it’s an XML file extension.