What is the primary function of XML?

The primary function of XML (eXtensible Markup Language) is to define a markup language that is flexible and can be tailored for specific applications. XML provides a framework for encoding documents in a format that is both human-readable and machine-readable. It allows developers to create custom tags that describe the data’s structure and meaning, making it particularly useful for data interchange between systems and applications.

The flexibility of XML is a key strength because it enables users to define their own markup languages tailored to the specific needs of their applications, unlike other markup languages that come with predefined tags. This capability is essential in contexts such as web services, data storage, and configuration files where data needs to be easily shared and interpreted by different systems.

Other options are related to distinct concepts. Creating documents with fixed formatting pertains more to HTML or specific document formats rather than XML's flexible nature. CSS is focused on styling and layout of web pages, which is separate from XML’s data representation function. Lastly, creating visual designs for software interfaces involves design principles and graphic elements rather than data interchange, which is the central role of XML.