The XML data document can either be produced manually or generated using server-side scripts that are connected to your databases or live data sources.
Here are a few basic things to know about XML data:
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 XML stands for Extensible Markup Language and is a text-based markup language derived from Standard Generalized Markup Language (SGML).
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XML allows you to create your own self-descriptive tags, or language, that suits your application as well as allows you to store the data irrespective of how it will be presented.
 - XML tags are case sensitive. The tag <Letter> is different from the tag <letter>. Opening and closing tags must be written with the same case.
 
XML elements must follow these naming rules:
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Names can contain letters, numbers, and other characters.
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Names cannot start with a number or punctuation character.
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Names cannot start with the letters xml (or XML, or Xml, etc).
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Names cannot contain spaces.