XML declaration example

<?xml version = "1.0" encoding = "UTF-8" standalone = "yes"?>

XML document can optionally have an XML declaration. XML document without declaration is also valid

<student>
   <name>George</name>
   <city>Tbilisi</city>
   <phone>(011) 123-4567</phone>
</student>

If the XML declaration is included, it must contain version number attribute

<?xml encoding="UTF-8" standalone="no"?>
<student>
   <name>George</name>
   <city>Tbilisi</city>
   <phone>(011) 123-4567</phone>
</student>

It will generate the following error:

error on line 1 at column 7: Malformed declaration expecting version

The names are always in lower case

<?xml Version="1.0" encoding="UTF-8" standalone="no"?>
<student>
   <name>George</name>
   <city>Tbilisi</city>
   <phone>(011) 123-4567</phone>
</student>

It will generate the following error:

error on line 1 at column 7: Malformed declaration expecting version

The XML declaration must begin with

<?xml

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

The following error will be generated:

error on line 1 at column 3: xmlParsePI : no target name

If document contains XML declaration, it must be the

first statement

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

The error will be the following:

error on line 6 at column 6: XML declaration allowed only at the start of the document

The order of placing the parameters is important. The correct order is:

version

,

encoding

and

standalone

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

This will generate the following error:

error on line 1 at column 7: Malformed declaration expecting version

Either single or double quotes may be used. Here is valid XML document

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

An HTTP protocol can override the value of encoding that we put in the declaration.

XML Attribute

specifies a single property for the element, using a

name/value

pair. An XML-element can have

one or more

attributes

<a href = "http://www.applications.ge/">Applications.ge</a>

In the example

href

is the

attribute name

and

http://www.applications.ge

is the

attribute value

... XML attribute names (unlike HTML) are case sensitive. Which means that

HREF

and

href

are considered two different XML attributes

<?xml version="1.0"?>
<student>
    <a href="http://www.applications.ge/" hreF="HTTP://applications.ge/">Applications.ge</a>
</student>

Several different values for the same attribute is not allowed. An attribute name must not appear more than once in the same tags:

<?xml version="1.0"?>
<student>
    <a href="http://www.applications.ge/" href="HTTP://applications.ge/">Applications.ge</a>
</student>

The following error will appear on the browser

error on line 3 at column 73: Attribute 
href
 redefined

Attribute names must always be defined without quotation marks, whereas attribute values must always appear in single or double quotation marks

<?xml version="1.0"?>
<student>
    <a "href"="http://www.applications.ge/">Applications.ge</a>
</student>

The following error will appear:

error on line 3 at column 8: error parsing 
attribute name
 

Attribute values must always be in quotation marks (single

'

or double

"

quotes)

<?xml version="1.0"?>
<student>
    <a href=http://www.applications.ge/>Applications.ge</a>
</student>

This incorrect syntax will generate the following error:

error on line 3 at column 13: AttValue: " or ' expected

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 -

"

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

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 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>

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.

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 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

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>