An Introduction To XML
XML is the 'Extensible Markup Language'. This is a general purpose markup language, designed to support a multitude of applications. It is a flexible text format, and was originally derived from SGML (standard ISO 8879).
It was designed to describe data, but unlike html (which it complements), tags are not predefined. It uses a 'Document Type Definition' (sometimes called a DTD) or an 'XML Schema' to actually describe the data.
A sample xml file:
Why Is XML Used?
XML is useful in a whole raft of situations. For example, using XML, data is actually stored outside your HTML. This in turn makes it much easier to share data, for example between incompatible systems, via plain text files, and so on. This opens up countless opportunities. Other strengths are that it is simultaneously a human and machine-readable format, and it is self documenting.
The latest updates to XML were made in August of 2006, when the 4th edition of XML 1.0 was published, along with the 2nd edition of XML 1.1 (these being the two recognized versions of XML).
It was designed to describe data, but unlike html (which it complements), tags are not predefined. It uses a 'Document Type Definition' (sometimes called a DTD) or an 'XML Schema' to actually describe the data.
A sample xml file:

Why Is XML Used?
XML is useful in a whole raft of situations. For example, using XML, data is actually stored outside your HTML. This in turn makes it much easier to share data, for example between incompatible systems, via plain text files, and so on. This opens up countless opportunities. Other strengths are that it is simultaneously a human and machine-readable format, and it is self documenting.
The latest updates to XML were made in August of 2006, when the 4th edition of XML 1.0 was published, along with the 2nd edition of XML 1.1 (these being the two recognized versions of XML).