===== XML Cheat Sheet =====

I stumble across XML documents intermittently and every time I need to review the basics again. This is a cheat sheet so that I can review it whenever I need to. Information here is a summarized form of the [[http://www.w3schools.com/xml/default.asp | XML Tutorial]]

==== What is XML ====

E**X**tensible **M**arkup **L**anguage (XML) is a markup language designed to describe data. It has no predefined tags and uses a Document Type Definition (DTD) or an XML Schema to describe the data. An XML document together with its DTD or XML Schema is self-descriptive.

XML uses text files to store data and can be used to create new languages e.g. WAP, WML, XHTML etc.

==== XML Syntax ====

A simple XML document :

<code>
<?xml version="1.0" encoding="ISO-8859-1"?>
<note date="12/11/2002">
<to>Tove</to>
<from>Jani</from>
<par>Hi.</par>
<par>Bye.</par>
</note>
</code>

  * The first line is an XML declaration which defines the XML version and the character encoding used in the document.

  * XML tags are case-sensitive and must have a corresponding closing tag. Tags must be properly nested.

  * An XML document must have a root element (note in the above). All elements may have child elements.

  * XML documents can be extended by adding new element types. Implementations must ignore unknown element types.

  * Whitespace is preserved. CR/LF is converted into just LF (UNIX format line terminators).

  * <!-- This is a comment -->

==== XML Elements ====

XML Elements can have attributes which must be either single or double quoted e.g. date in the above.

Elements can have either
  * Empty content
  * Simple content(text ony)
  * Element content (child elements)
  * Mixed content (child elements and text)

Elements can be parents, children or siblings of other elements.

XML element names can contain any character except for a space but must start with a letter and can't start with xml (in any case). Names shoud not include . : or - .