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Valeri Tandilashvili's XML Notes
Results: 23
XML CDATA Rules
1. 
CDATA
cannot contain the string 
]]>
anywhere in the XML document 2. 
Nesting
is not allowed in CDATA section
XML Processing Instructions (PIs)
XML Processing instructions allow documents to contain instructions for applications. PI consists of two parts: 1. 
target
- Identifies the application to which the instruction is directed. 2. 
instruction
- A character that describes the information for the 
target
application to process. ... PI's example in real XML document
<?xml version="1.0" encoding="UTF-8"?>
<student>
    <?sort alpha-ascending?>
    <?textinfo whitespace is allowed ?>
    <first-name>George</first-name>
    <phone.mobile>(011) 123-4567</phone.mobile>
</student>
In this example we have two PIs 1. 
sort
with value - 
alpha-ascending
2. 
textinfo
with value - 
whitespace is allowed
... Note: processing instructions can contain any data except the combination 
?>
, which is interpreted as a closing delimiter
XML White Spaces
There are 3 types of whitespace within an XML document, XML Syntax, Significant and Insignificant
1. XML Syntactical whitespace - is whitespace required by the XML in order to delimitate XML constructs.

2. Insignificant Whitespace - is whitespace, that is not considered part of an element, if two elements are separated by just whitespace its considered insignificant.

3. Significant Whitespace - is whitespace that XML element attribute contains.
XML Comments Rules
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.
XML Tags Rules
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>
XML DOM - XMLHttpRequest
The example below parses an XML document 
address.xml
into an XML DOM object. Then extracts 
contact
information using 
JavaScript
<!DOCTYPE html>
<html>
   <body>
      <h1>TutorialsPoint DOM example </h1>
      <div>
         <b>Name:</b> <span id = "name"></span><br>
         <b>Company:</b> <span id = "company"></span><br>
         <b>Phone:</b> <span id = "phone"></span>
      </div>
      <script>
         if (window.XMLHttpRequest)
         {// code for IE7+, Firefox, Chrome, Opera, Safari
            xmlhttp = new XMLHttpRequest();
         }
        //  else
        //  {// code for IE6, IE5
        //     xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        //  }
         xmlhttp.open("GET","address.xml",false);
         xmlhttp.send();
         xmlDoc = xmlhttp.responseXML;

         document.getElementById("name").innerHTML = xmlDoc.getElementsByTagName("name")[0].childNodes[0].nodeValue;
         document.getElementById("company").innerHTML = xmlDoc.getElementsByTagName("company")[0].childNodes[0].nodeValue;
         document.getElementById("phone").innerHTML = xmlDoc.getElementsByTagName("phone")[0].childNodes[0].nodeValue;
      </script>
   </body>
</html>
address.xml
file content
<?xml version = "1.0"?>
<contact>
   <name>Tanmay Patil</name>
   <company>TutorialsPoint</company>
   <phone>(011) 123-4567</phone>
</contact>
XML encoding
There are two the most commonly used Encoding Types for XML documents: 1. 
UTF-8
- 8-bits are used to represent a character 2. 
UTF-16
- 16-bits are used to represent a character ... 
UTF
stands for 
UCS Transformation Format
, and UCS itself means 
Universal Character Set
... XML document example that has 
UTF-8
encoding
<?xml version="1.0" encoding="UTF-8"?>
<student>
    <first-name>George</first-name>
    <phone.mobile>(011) 123-4567</phone.mobile>
</student>
Note: If an XML document has not specified encoding, the default is 
UTF-8
XML - get PI's values using PHP
The code below can be used to get PI's value from an XML document
<?php

$my_xml_data = 
'<?xml version="1.0" encoding="UTF-8"?>
<student>
    <?sort alpha-ascending?>
    <?textinfo whitespace is allowed ?>
    <first-name>George</first-name>
    <phone.mobile>(011) 123-4567</phone.mobile>
</student>';

$xml = simplexml_load_string($my_xml_data);

$doc   = dom_import_simplexml($xml)->ownerDocument;
$xpath = new DOMXPath($doc);

# prints "/* processing instructions */ ", the value of the first PI: textinfo
echo $xpath->evaluate('string(//processing-instruction("textinfo")[1])');
The output of the above code is the following:
whitespace is allowed
XML comments
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>
XML empty tags
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.
Results: 23