Besides the fact that XML is a widely accepted standard, several other attributes of XML contribute to its rapid acceptance and growing popularity:
Most importantly, XML is extensible. An XML document can grow to include and describe more data, yet each application that uses the document need only be concerned with the XML content that matters to it.
XML is self-describing. The markup and hierarchical structure of the XML document can in some cases be interpreted by applications that do not know ahead of time what to expect from the document.
XML is simple text. This fact makes it suitable and safe for transferring across platforms and operating systems that do not readily share more complex document types. As text, XML can also be readily displayed and edited in simple editors.
XML is robust. It can describe any kind of data with the help of its associated schema-description languages.
XML is easy to learn, easy to read, and easy to understand.
Most importantly, XML is extensible. An XML document can grow to include and describe more data, yet each application that uses the document need only be concerned with the XML content that matters to it.