* XML stands for eXtensible Markup Language
* subset of the Standard Generalized Markup Language (SGML) defined in
ISO standard 8879:1986
* makes documents interchangeable across the web - it's a language that every browser can decipher
* however, it is not HTML or CSS language, nor is it a template for web design
* XML is a formal language that computers use to talk to each other about the components of documents (all kinds: books, memos, etc.)
* though it is NOT HTML, it surprisingly looks a lot like it. :-)
* based on the concept of "documents" composed of a series of "entities"
* users create their own definitions of what tags mean, and then code that into the document schema
* the original XML schema language is the Document Type Definition (DTD); however, this is kind of bulky and awkward and many web designers are not fond of it. Many other new schema languages have emerged that are more favorable, such as RELAX NG.
* there are many different types of elements that are used in XML schema. Some are simple, and contain only text. Others are more complex, wherein elements can be combined together into a single element, or can even be empty.
* an example of a complex element that contains other elements:
* string data types are used for values that contains character strings. The string data type can contain characters, line feeds, carriage returns, and tab characters.
* even though you CAN code your own XML, it's much to your benefit to use an editing software. It can help catch your errors (like forgetting to close elements) and can also help guide your work.