19.1. The Basic Concepts
The most important thing you have to know about XML is that XML is a metamarkup language for text documents. XML is not a programming language, which means that it is not possible to write standalone applications that need nothing other than XML—it has nothing to do with languages such as C and Perl. XML is a language like HTML or SGML and can be used to describe documents.
One of the biggest advantages of XML over other languages for describing documents is that it does not have a fixed set of tags because this would be far too inflexible. Working with a fixed set of tags would fail because the reality cannot be modeled using just a few static commands.
19.1.1. XML Technologies
Many technologies have been developed on ...