XML Syntax Rules

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XML
Syntax Rules


The syntax rules of XML
are very simple and logical. The rules are easy to learn, and easy to use.


1.     All XML Elements Must Have a Closing
Tag


In
XML, it is illegal to omit the closing tag. All elements must have a
closing tag:



<p>This is a paragraph</p>

<p>This is another paragraph</p>

 


2.     XML Tags are Case Sensitive


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


3.     XML Elements Must be Properly Nested


In
XML, all elements must be properly nested within each other:



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

 


4.     XML Documents Must Have a Root
Element


XML
documents must contain one element that is the parent of all other
elements. This element is called the root element.



<root>

  <child>

    <subchild>.....</subchild>

  </child>

</root>

 


5.     XML Attribute Values Must be Quoted


<note date="12/11/2007">

  <to>Tove</to>

  <from>Jani</from>

</note>


6.     Entity References


Some characters have a
special meaning in XML.


If you place a character
like "<" inside an XML element, it will generate an error because
the parser interprets it as the start of a new element.


To
avoid this error, replace the "<" character with an entity
reference:



<message>if salary &lt; 1000
then</message>

There
are 5 predefined entity references in XML:



&lt;

< 

less than

&gt;

> 

greater than

&amp;

&

ampersand 

&apos;

'

apostrophe

&quot;

"

quotation mark

Note: Only the characters "<" and
"&" are strictly illegal in XML. The greater than character is
legal, but it is a good habit to replace it.


 


7.     Comments in XML


The syntax for writing
comments in XML is similar to that of HTML.


<!-- This is a comment
-->


 


8.     White-space is Preserved in XML


HTML
truncates multiple white-space characters to one single white-space:



HTML:


Hello      
    Tove


Output:


Hello Tove

With
XML, the white-space in a document is not truncated.


 


9.     XML Stores New Line as LF


In Windows applications, a
new line is normally stored as a pair of characters: carriage return (CR) and
line feed (LF). In Unix applications, a new line is normally stored as a LF
character. Macintosh applications also use an LF to store a new line.


XML stores a new line as
LF.


 


hildren:
<title>,< author>, <year>, <price>.


for more info go to : http://www.w3schools.com/xml/

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