XML Comments and CDATA Sections:

Adding Comments in XML Documents:

A Comments are used to include notes or explanations within the document that are not processed by the XML parser.

Comments can be helpful for providing context or documentation within the XML code.

Syntax:

Comments start with .
Comments cannot contain the string '--' within them.

Example:

                    
<!-- This is a comment -->
<book>
  <title>XML Fundamentals</title>
  <author>John Smith</author>
  <!-- The price of the book -->
  <price>29.99</price>
</book>

In this example:

This  is a comment before the <book> element.
And this  is a comment before the <price> element.

Using CDATA Sections to Include Special Characters and Raw Text:

CDATA sections are used for embedding text blocks, which should not be parsed by the XML parser. It is good for including contents that contain characters treated as XML markup such as < and &.

Syntax:

<![CDATA[ initiated and terminated CDATA sections.
Everything contained in a CDATA section is treated as unprocessed text.

Example:

                    
<description>
  <![CDATA[
  This book covers:
  - XML Basics
  - XML Syntax
  - Advanced XML topics
  <note>Make sure to practice!</note>
  ]]>
</description>

In this example, <<<< >>>> are part of the content within <![CDATA[ ]]> but remain in the same format they were placed unlike when they would have been treated as tags.

Summary:

Comments:  is employed to put comments or notes inside XML documents. These comments do not appear on the structure of an XML document nor its contents; the parser ignores them.
CDATA Sections: <![CDATA[ ]]> incorporates unescaped raw text and special characters. Whatever found within a CDATA section is considered character data rather than XML markup.

Understanding how to use comments and CDATA sections in XML helps in making the documents more readable and in handling special content without parsing issues.