Editing WoW:AddOn programming tutorial/Introduction (section)

==== Blizzard XML format declared ====
For those of you who don't know, XML stands for eXtensible Markup Language and is a means of tagging content with identifiers. What the identifiers are and how they are organized can be defined in something called a Schema. In our case, we want to create XML documents that WoW will understand, so we will use the Schema provided by Blizzard for the Wow User Interface.

We declare that our document conforms to the Blizzard schema with the following bit of magic:

 <nowiki><Ui xmlns="http://www.blizzard.com/wow/ui/" 
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
                   xsi:schemaLocation="http://www.blizzard.com/wow/ui/ 
                   ..\..\FrameXML\UI.xsd"></nowiki>
 
 </Ui>

The exact meaning of all of the above is beyond the scope of this tutorial. Consider it a magic formula that you always put in every .xml file you will create for the WoW user interface. For those of you that like to reformat things, the first three lines can be merged into one line (use spaces), but the fourth line (..\..\FrameXML\UI.xsd"> ) needs to be on a line by itself starting in column 1.

There are a few general notes that you need to know about concerning XML, particularly as it is used by WoW. The generalized format of a tag is:

 <tagname attribute="attribute value" anotherattribute="anotherattribute value">
 
 </tagname>

A tag must have a tagname, and it may have zero or more attributes along with the attributes' associated values in double quotes. The tag is everything between the ''''<tagname'''' and the trailing ''''>''''. The tag is closed by an end tag with the same name as tag: ''''</tagname>''''. Tagnames do not have spaces, are case sensitive, start with a capital letter, and additional words are also capitalized. A valid tagname might be 'BackgroundWidgets', while 'backgroundwidgets' would not be valid. Blizzard defines all valid tagnames in their UI.xsd. The [[XML user interface]] page has a good list under [[XML user interface#Widget Elements|Widget Elements]] which will aid you until we get further along.

Everything between the tag and the end tag is content to the tag. Everything. Even other tags along with their content. In the case where there is no content to a tag, the end of the tag has ''''/>'''' instead of just ''''>'''' and there is no separate end tag. A complete tag with no content looks like:

 <tagname attribute="attribute value" anotherattribute="anotherattribute value"/>

Using the below piece of magic as an example, we can see that it is a tag with the name ''''Ui'''' and it has three attributes (the funny fourth line is a part of the prior attribute). Content is represented by the space between the end of the tag (the ''''>'''' on the fourth line) and the ''''</Ui>'''' end tag.