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XML Syntax

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An example XML document:

<?xml version="1.0"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

The first line in the document: The XML declaration should always be included. It defines the XML version of the document. In this case the document conforms to the 1.0 specification of XML: 

<?xml version="1.0"?>

The next line defines the first element of the document (the root element): 

<note>

The next lines defines 4 child elements of the root (to, from, heading, and body):

<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>

The last line defines the end of the root element:

</note>

All XML elements must have a closing tag

In HTML some elements do not have to have a closing tag. The following code is legal in HTML:

<p>This is a paragraph
<p>This is another paragraph

In XML all elements must have a closing tag like this:

<p>This is a paragraph</p>
<p>This is another paragraph</p> 

XML tags are case sensitive

XML tags are case sensitive. The tag <Letter> is different from the tag <letter>.

Opening and closing tags must therefore be written with the same case:

<Message>This is incorrect</message>
  
<message>This is correct</message>

All XML elements must be properly nested

In HTML some elements can be improperly nested within each other like this:

<b><i>This text is bold and italic</b></i>

In XML all elements must be properly nested within each other like this

<b><i>This text is bold and italic</i></b>

All XML documents must have a root tag

All XML documents must contain a single tag pair to define the root element. All other elements must be nested within the root element. All elements can have sub (children) elements. Sub elements must be in pairs and correctly nested within their parent element:

<root>
  <child>
    <subchild>
    </subchild>
  </child>
</root>

Attribute values must always be quoted

XML elements can have attributes in name/value pairs just like in HTML. In XML the attribute value must always be quoted. Study the two XML documents below. The first one is incorrect, the second is correct:

<?xml version="1.0"?>
<note date=12/11/99>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

<?xml version="1.0"?>
<note date="12/11/99">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
 
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