XML(5) PCDATA, CDATA, escaping illegal character

PCDATA

Simply speaking, PCDATA stands for Parsed Character Data. That means the characters are to be parsed by the XML, XHTML, or HTML parser. (< will be changed to <, <p> will be taken to mean a paragraph tag, etc). Compare that with CDATA, where the characters are
not to be parsed by the XML, XHTML, or HTML parser.

CDATA

The term CDATA, meaning character data, is used for distinct, but related purposes in the markup languages SGML and XML. The term indicates that a certain portion of the document is general character data, rather than non-character data or character data with
a more specific, limited structure.

CDATA Sections

If there are lots of escaping characters, the output would be very ugly, CDATA stands for character data, is used to tell the XML parser not to parse the text.

<comparison><![CDATA[6 is < 7 & 7 > 6]]></comparison>

When you use <!CDATA[  ]]> the XML parser(IE) will parse the illegal characters correctly!

Special Characters

These characters are illegal characters you have to escape:
&—the & character
<—the < character
>—the > character
'—the ' character
"—the " character