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In XML to read and update, create and manipulate an XML document, we will need
an XML parser that will parse or validate all the XML document with standards of
W3C. The parser loads the document into our computer's memory and when the
document is loaded, its data can be manipulated using the DOM Document Object
Model. The DOM treats the XML document as a tree that's why we can see an XML
document in web browser as a tree.
Now the
only content inside a CDATA section of XML document will be ignored by the
XML parser. So when the parser parse the XML tags then it will also parse the
content or text in between tags are also parsed by it. As shown in example
below.
XML for CDATA Example
<employee>
<firstName>Creston</firstName>
<lastName>Narvon</lastName>
<gender>m</gender>
<DOB>22/04/1976</DOB>
</employee>
On
above XML code all the tags like <employee> <firstName> <lastName> <gender> and <DOB>
will be parse by the XML parser and its content like Creston, Narvon, m and
22/04/1976 will also be parse by the XML parser. Parser observe the tags
and match them with XML standards. Like <firstName> is embeded in <employee>
root tag and that's why in web browser we can see it as tree.
XML Parser Issues.
Some
character are illegal in XML to use them like "<" less then sign and " quotes and
grater then ">" sign & and sign, single quote ' or Apostrophes. As we use
the less then < sign in below example, it is not a valid XML document and it
will be appear having an error in browser.
Invalid XML CDATA
<employee>;
<firstName>"Creston"</firstName>
<salary>salary is < 3100 </salary>
</employee>
On above example of invalid XML we can see we use " around the Creston and it is not a valid way to
define content of XML tags. and in [Salary is < 3100] we used < sign it is also
not allowed. In
two character are < and & sign are strictly illegal so when ever we will use
these parser will not allow. Solution for this is, we will use XML CDATA
as an XML section and here we can use the < and & sign and others like > double
quotes " and single quotes '.
Valid XML CDATA Example
<script>
<![CDATA[
function checksalary(salary)
{
if (salary < 3100) than
{
return true
}
else
{
return false
}
}
]]>
</script>
As we tried to used < sign on the example at the top of page of this
section of XML Tutorial and XML parser
generate the error now on above example we can use these characters as shown and
parser will ignore them all.
Between the start of the section, "<![CDATA[" and the end of the section, "]]>",
all character data is passed directly to the application. The only string that cannot occur in a
CDATA section is "]]>". Comments are not recognized in a CDATA section. If present, the literal text
"<!--comment-->" will be passed directly to the application. The character string ]]> is
not allowed within a CDATA block as it would signal the end of the CDATA block. CDATA
does not work in HTML.
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