XML Reference

📄 What is XML?

XML (eXtensible Markup Language) is a markup language for storing and transporting data. It's both human-readable and machine-readable, making it perfect for data exchange between systems.


<?xml version="1.0" encoding="UTF-8"?>
<message>
    <text>Hello XML!</text>
</message>

XML Syntax Rules

XML follows strict syntax rules that ensure documents are well-formed and valid. Understanding these fundamental rules is essential for creating proper XML documents that can be parsed correctly by any XML processor.

🏷️

Tags Must Close

Every opening tag needs a closing tag

<book>Content</book>

🔤

Case Sensitive

Tags are case-sensitive

<Book> ≠ <book>

🌳

Proper Nesting

Elements must be properly nested

<a><b>Text</b></a>

🌲

Root Element

One root element required

<root>...</root>

🔹 Basic XML Document

A complete XML document with declaration and structure:

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
    <book category="fiction">
        <title>The Great Gatsby</title>
        <author>F. Scott Fitzgerald</author>
        <year>1925</year>
        <price>10.99</price>
    </book>
</bookstore>

Structure:

Declaration: <?xml version="1.0"?>

Root: bookstore

Child: book (with attribute)

Data: title, author, year, price

🔹 XML Elements

Elements are the building blocks of XML documents:

<!-- Element with content -->
<name>John Doe</name>

<!-- Empty element (two ways) -->
<linebreak></linebreak>
<linebreak />

<!-- Nested elements -->
<person>
    <firstname>John</firstname>
    <lastname>Doe</lastname>
</person>

🔹 XML Attributes

Attributes provide additional information about elements:

<!-- Single attribute -->
<book category="fiction">Title</book>

<!-- Multiple attributes -->
<img src="photo.jpg" alt="Photo" width="500" />

<!-- Attributes vs Elements -->
<person gender="female">
    <firstname>Anna</firstname>
    <lastname>Smith</lastname>
</person>

Attribute Rules:

Must be quoted (single or double quotes)
Cannot contain multiple values
Cannot contain tree structures
Not easily expandable

🔹 XML Namespaces

Namespaces prevent element name conflicts:

<?xml version="1.0"?>
<root xmlns:h="http://www.w3.org/HTML"
      xmlns:f="http://www.example.com/furniture">
    
    <h:table>
        <h:tr>
            <h:td>Cell</h:td>
        </h:tr>
    </h:table>
    
    <f:table>
        <f:name>Coffee Table</f:name>
        <f:width>80</f:width>
    </f:table>
    
</root>

🔹 XML Comments

Add comments to document your XML:

<?xml version="1.0"?>
<!-- This is a comment -->
<data>
    <!-- Multi-line comment
         can span multiple lines
         for detailed explanations -->
    <item>Value</item>
</data>

🔹 Special Characters

Escape special characters using entities:

<message>
    <text>Price: 5 &lt; 10</text>
    <quote>&quot;Hello&quot;</quote>
    <company>AT&amp;T</company>
</message>

Entity References:

< = < (less than)
> = > (greater than)
& = & (ampersand)
" = " (quote)
' = ' (apostrophe)

🔹 CDATA Sections

Use CDATA for text containing special characters:

<script>
<![CDATA[
    function compare(a, b) {
        if (a < b) {
            return -1;
        }
        return 1;
    }
]]>
</script>