XML Validator, Formatter, and Minifier

What is XML?

• XML (Extensible Markup Language) is a markup language like HTML for storage or transmission of data.


• XML is widely used in web services to transport data over the network.


• XML has no predefined tags, unlike HTML.


• XML is very easy to parse and generate.


• XML provides strong support for unicode characters. The default character encoding is UTF-8 for XML documents.


• XML defines set of rules for encoding documents in a format which are human-friendly.


• XML is widely used in a SOA (Services Oriented Architecture).


• XML files have the extension .xml and the media types of XML are application/xml and text/xml


• Almost all major programming languages supports XML due to its language-independent data format.

Structure of a XML document:

1. A XML document contain exactly one root element which is the start tag of the XML document and it contains all other elements.
   
   

   <root>
   	<section>
   		<sub-section></sub-section>
   		<sub-section></sub-section>
   	</section>
   
   	<section>
   		<sub-section></sub-section>
   		<sub-section></sub-section>
   	</section>
   <root>

    
2. XML documents may begin with a prolog that appears before the root element. It has the metadata about the XML document, such as character encoding, document structure, and style sheets. For example,
   
   

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

    
3. A tag in XML is a case-sensitive markup construct that begins with < and ends with >. A tag can be:
   
   
   • A start-tag, such as <name>;
   • A end-tag, such as </name>;
   • An empty-element tag, such as <name/>.
    
 
4. An element in XML is formed by characters between the start-tag and the end-tag. For example, <name>John Snow</name>. It can also consists only of an empty-element tag. For example, <name/>.  
 
5. XML elements can have attributes which exists within a start-tag or empty-element tag. An attribute consist of a name–value pair. For example, <img src="screenshot.png" alt="screenshot" />. Here the names of the attributes are src and alt, and their values are screenshot.png and screenshot respectively.

Syntax Rules:

1. Each start-tag in XML must have a matching end-tag and all tags should be properly nested, with none missing and none overlapping. The tag names cannot contain any of the characters !"#$%&'()*+,/;<=>?@[\]^`{|}~, nor a space character, and cannot begin with "-", ".", or a number.  
 
2. The characters < and & holds special meaning in XML. They are key syntax characters and should not be used in an element outside a CDATA section. XML provides escape facilities to handle these special characters. For example:
   
   
   • &lt; represents <;
   • &amp; represents &.
   
   XML has three other predefined entities:
   
   
   • &gt; represents >;
   • &apos; represents ';
   • &quot; represents ".
    
 
3. A XML document cannot contain any whitespace before the XML declaration else it will be treated as a processing instruction by the parser. XML processors preserve all white space in element content, while all whitespace within the attribute values are reported as single spaces.  
 
4. Similar to HTML, a comment in XML begins with <!-- and ends with -->.