The term

CDATA

means,

Character Data

. CDATA is defined as blocks of text that

are not parsed

by the parser, but are otherwise recognized as markup

<?xml version="1.0" encoding="UTF-8"?>
<student>
    <!-- Some comment about the student -->
    <first-name>George</first-name>
    <phone.mobile>(011) 123-4567</phone.mobile>
    <city />
    <description>
        <![CDATA[
            <p>
            <a href="/mylink/article1"><img style="float: left; margin-right: 5px;" height="80" src="/mylink/image" alt=""/></a>
            Author Names
            <br/><em>Date</em>
            <br/>Paragraph of text describing the article to be displayed</p>
        ]]>        
    </description>
</student>

CDATA Start section

- CDATA begins with the nine-character delimiter

<![CDATA[

CDATA End section

- CDATA section ends with

]]>

delimiter

CData section

- Characters inside

CData

section are interpreted as characters, and not as markup. It may contain markup characters

<

,

>

, and

&

, but they are ignored by the XML processor

Rules that should be followed when we use XML comments:

- Comment must appear after XML declaration.
- Comment may appear anywhere in a document
- Comment must not appear within attribute values.
- Comment cannot be nested inside the other comment.

Similar to HTML comments, XML comment has the following syntax:

<!-- Our comment -->

XML comment example in XML document:

<?xml version="1.0" encoding="UTF-8"?>
<student>
    <!-- Some comment about the student -->
    <first-name>George</first-name>
    <phone.mobile>(011) 123-4567</phone.mobile>
    <tive_language>English</tive_language>
    <another_tag>some text</another_tag>
    <city />
</student>

- An element name can contain any alphanumeric characters. Allowed

symbols

in names are the hyphen

-

, under-score

_

, period

.

and digits

0-9

- Names are

case sensitive

, Address, address, and ADDRESS are different names. - Start and end tags of an element must be

the same

. - An element, which is a container, can contain

text

or

elements

<?xml version="1.0" encoding="UTF-8"?>
<student>
   <first-name>George</first-name>
   <phone.mobile>(011) 123-4567</phone.mobile>
   <native_language>English</native_language>
   <city />
</student>

Note: XML element name must not start with

.

,

-

,

digit

The symbols: hyphen

-

, under-score

_

and period

.

are allowed in element name. The XML example is valid

<?xml version="1.0" encoding="UTF-8"?>
<student>
   <first-name>George</first-name>
   <phone.mobile>(011) 123-4567</phone.mobile>
   <native_language>English</native_language>
   <city />
</student>

An empty element in XML document can be represented in two ways:

<?xml version="1.0" encoding="UTF-8"?>
<student>
   <name>George</name>
   <phone>(011) 123-4567</phone>
   <address></address>
   <city />
</student>

One way is

<address></address>

element and another is

<city />

. In other words, one with closing tag and another is self-closing tag.

XML tags are

case-sensitive

- because of the case difference in two tags, which is treated as incorrect syntax in XML

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<student>
   <name>George</name>
   <city>Tbilisi</city>
   <phone>(011) 123-4567</phone>
   <address>Wrong syntax</ADdress>
   <hr />
</student>

This will generate the error:

error on line 6 at column 23: Opening and ending tag mismatch: address line 0 and ADdress

XML tags must be closed

in an appropriate order

, which means an XML element opened inside another element must be closed before the outer element

<outer_element>
   <internal_element>
      Right, because the inner tag is closed before the outer
   </internal_element>
</outer_element>

version 

- specifies the version used in the XML document (1.0)

encoding

- defines the character encoding used in the XML document (UTF-8)

standalone

- if the value is

yes

it means there is no external declaration required to parse the document (yes)

XML references allow us to have symbols in XML text, that are not allowed to be included directly. References begin with the symbol

&

which is a reserved character and end with the symbol

;

XML has two types of references: ... 1.

Entity Reference

− which contains a name between the start and the end delimiters. For example

&

where amp is name. The name refers to

&

symbol. ... 2.

Character Reference

− contains reference, such as

A

contains a hash mark

#

followed by a number. The number refers to the Unicode code of a character. In this case, 65 refers to alphabet

A

Some characters are are not allowed in XML text because they are reserved by the XML itself. Hence, they cannot be used directly. If we need to include them in text, some replacement-entities are used. These symbols are:

<

- less than -

<

>

- greater than -

>

'

- ampersand -

&

"

- apostrophe -

'

&

- quotation mark -

"