Table of Content


What is HTML?

Imagine you want to create a website. HTML (HyperText Markup Language) is like the building blocks of a website. It's a code that tells the computer how to display text, images, videos, and other elements on your page.

What is XHTML?

XHTML (Extensible HyperText Markup Language) is a newer version of HTML that's stricter in its rules. It's like a more organized and precise version of HTML, making it easier for computers to understand the structure of your website.

The Relationship Between HTML and XHTML

HTML and XHTML are both languages used to create websites. However, XHTML is a stricter version of HTML that follows more specific rules.

Key Differences Between HTML and XHTML:

  • Format: HTML is case-insensitive, while XHTML is case-sensitive. For example, <p> (HTML) is equivalent to <P> (XHTML).
  • Closing Tags: HTML doesn't always require closing tags, such as <br> (line break). XHTML, however, requires all elements to have closing tags, such as <br/>.
  • Attributes: In HTML, attributes can be specified without values, such as <font size>. In XHTML, all attributes must have values, such as <font size="5">.

Why Use XHTML?

XHTML is a more precise and organized language than HTML. This makes it easier for:

  • Computers: To interpret the structure of your website.
  • Search engines: To index your website's content more accurately.
  • Developers: To collaborate on web projects more efficiently.

Which One Should You Use?

In general, it's recommended to use HTML5, which is the latest version of HTML, as it's more supported by modern browsers and provides additional features.

HTML Basics

Understanding HTML Code

HTML (HyperText Markup Language) is the language used to create web pages. It's like the building blocks of a website, telling the browser how to display text, images, links, and more.

Basic Structure of an HTML Document

Every HTML document has a basic structure:

  • <html> and </html>: The outer tags that wrap the entire document.
  • <head> and </head>: Contains information about the page, like its title and keywords.
  • <body> and </body>: Contains the visible content on the page, such as text, images, and links.

Common HTML Tags and Their Uses

Here are some common HTML tags and what they do:

Example: <h1>This is a Heading 1</h1>

Example: <p>This is a paragraph.</p>

Example: <br>This will break the line here.

Example: <a href="">Click here</a>

Example: <img src="image.jpg" alt="Image Alt Text">

Example: <ul><li>Item 1</li><li>Item 2</li></ul>

Example: <ol><li>Item 1</li><li>Item 2</li></ol>

Example: <table><tr><th>Name</th><th>Age</th></tr><tr><td>John</td><td>30</td></tr></table>

  • <h1> to <h6>: Heading tags for different levels of headings.
  • <p>: Creates a paragraph.
  • <br>: Line break.
  • <a>: Creates a link.
  • <img>: Inserts an image.
  • <ul>: Creates an unordered list.
  • <ol>: Creates an ordered list.
  • <table>: Creates Table

XHTML Fundamentals

Understanding XML Files

XML (Extensible Markup Language) is like a recipe that describes how to create a dish. In this case, the dish is a web page or document. It uses tags to define different parts of the page, like the title, headings, paragraphs, and images.

XHTML Document Structure

An XHTML document is like the recipe for a web page. It has the following structure:

  • XML Declaration: This is the beginning of the recipe. It tells the computer what type of document it is.
  • Document Type Definition (DTD): This tells the computer what rules the document has to follow.
  • Root Element: This is the main part of the recipe, where the actual content of the web page is described.

XHTML Syntax and Rules

The syntax and rules of XHTML are like the instructions for making the dish. They tell the computer how to read and interpret the XML tags.

  • Tags: Tags are enclosed in angle brackets, like <body> and </body>. They define different parts of the document.
  • Attributes: Attributes are added to tags to provide additional information, like <p align="center"> to center a paragraph.
  • Nesting: Tags can be nested inside each other, like <div><p>...</p></div> to create a section with a paragraph inside.
  • Closing Tags: Every opening tag must have a corresponding closing tag with a slash, like <h1>Hello</h1>.
  • Whitespace: Whitespace (spaces and line breaks) is not significant, so you can use it to make your document more readable.


Here is a simple XHTML document:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<title>My Web Page</title>
<h1>Welcome to My Page</h1>
<p>This is my first web page.</p>

This document creates a web page with the title "My Web Page". The body contains a heading and a paragraph.

Differences Between HTML and XHTML

Syntax Differences:

  • Syntax refers to the rules for writing code. Different programming languages have different syntax rules. For example, in Java we need to use curly braces { and } to enclose a block of code, but in Python we use indentation to do the same.
  • This means that even though two programs might do the same thing, they might look different because they use different syntax.

Structural Differences:

  • Structure refers to how code is organized and structured. Different programming languages can have different ways of organizing code, such as using classes, methods, and functions.
  • For example, in Java, we use classes to organize code, but in Python, we use functions and modules.

Validation and Compatibility:

  • Validation refers to checking whether code is correct and meets the rules of the programming language.
  • Compatibility refers to whether code can be used with other code or components.
  • Different programming languages have different tools and mechanisms for validation and compatibility. For example, Java uses a compiler to validate code and make sure it's compatible with other Java code, while Python uses an interpreter to validate and run code.

Advantages and Disadvantages of HTML


  • Flexibility and Accessibility: JSON allows you to organize data in any way you want, making it easy to create and modify data structures. It can be accessed from a wide range of programming languages and platforms, so you can work with JSON data in almost any environment.
  • Ease of Use and Compatibility: JSON is a human-readable format, so it's easy to understand and write. It's also compatible with many different programming languages and data processing tools, making it a versatile format for data exchange.


  • Potential for Validation Issues: JSON doesn't have any built-in validation mechanisms, so it's possible to create invalid JSON data that can lead to errors.
  • Semantic limitations: JSON is a data format, not a schema language. This means that it doesn't provide any semantics for the data it contains, so it's up to the application to interpret the meaning of the data.

Advantages and Disadvantages of XHTML


  • Strict syntax: XHTML's strict rules help to prevent errors and make your pages more reliable.
  • Compatibility: XHTML is compatible with older web browsers, which means your pages can be viewed by a wider audience.
  • Extensibility: You can use additional features or create your own custom tags to enhance your XHTML pages.


  • Complexity: XHTML's strict rules can make it more difficult to learn and use compared to other coding languages.
  • Limited flexibility: While XHTML is extensible, it doesn't offer the same level of flexibility as XML for creating custom data structures.
  • Legacy status: XHTML is considered a legacy language, with newer technologies like HTML5 and CSS3 being more commonly used today.

Best Practices for HTML and XHTML

Heading Tags (H1-H6)

Heading tags are like titles for different sections of a web page. They help organize content and make it easier to skim.

  • H1 is the most important heading, like the title of the whole page.
  • H2 is for subheadings, like the titles of different sections.
  • H3-H6 are for further divisions, like subsections or paragraphs.


<h1>My Website</h1>
<h2>About Me</h2>
<h3>My Skills</h3>
<h4>Front-End Development</h4>

Meta Tags

Meta tags provide information about a web page to search engines and browsers. They don't appear on the page itself, but they help with things like:

  • SEO (Search Engine Optimization): They tell search engines what the page is about, helping it rank higher in results.
  • Web accessibility: They provide information about the language, keywords, and description for assistive technologies.


<meta name="description" content="My website is about my skills and interests." />
<meta name="keywords" content="web development, HTML, CSS" />
<meta name="language" content="en" />

HTML and XHTML Entities

HTML and XHTML entities are special characters that cannot be typed directly, such as accents (é), special symbols (©), and non-breaking spaces ( ). They need to be encoded using special characters.


  • Accent: é (é)
  • Copyright symbol: ©
  • Non-breaking space:  

Proper Use for Web Accessibility and SEO

  • Headings: Use headings to structure your content logically and make it easy to navigate.
  • Meta tags: Provide accurate information in meta tags to help search engines and assistive technologies understand your page.
  • HTML entities: Use HTML entities to display special characters that are not available on a standard keyboard.

Common Mistakes to Avoid

Using Outdated or Invalid Tags

Imagine you're writing a letter, but you're using an old pen that doesn't work well or even a fake pen. Your letter won't be clear or understood by the person who reads it. In website programming, outdated or invalid tags are like old or fake pens. They won't work properly and can make your website look messy or confusing.

Neglecting Browser Compatibility

Websites are like drawings that everyone wants to see. But just like different people have different pencils and crayons, different computers have different ways of displaying websites. If you don't make your website compatible with different computers (browsers), then some people won't be able to see your beautiful drawing.

Ignoring Semantic Structure and Accessibility

When you write a paragraph, you use certain words and phrases to make it easy for people to understand. You don't use fancy language that nobody knows or jumble everything together. Websites should be like that too. Proper structure and accessibility make it easy for everyone, even people with disabilities, to understand your content.

Overcomplicating Code with Unnecessary Tags

Imagine writing a letter and using a lot of extra words or fancy fonts that make it hard to read. Website programming also has a similar problem. Sometimes, people write code with too many extra tags that make the website slow and difficult to understand. It's like adding extra paragraphs and special characters to a letter that aren't really needed.

HTML and XHTML in Web Development

HTML and XHTML in Web Design

HTML (HyperText Markup Language) is like the building blocks of a website. It defines the structure and content of a web page.

XHTML (Extensible HyperText Markup Language) is a stricter version of HTML that follows XML (Extensible Markup Language) rules.

CSS for Styling

CSS (Cascading Style Sheets) is like a stylist for your website. It controls the appearance of your web page, such as the font size, color, and layout.

JavaScript for Interactivity

JavaScript is a programming language that makes your website interactive. It allows you to add things like:

  • Pop-up boxes
  • Drop-down menus
  • Image sliders
  • Games

Combining HTML, CSS, and JavaScript

Think of it like this:

  • HTML is the foundation of your house.
  • CSS is the paint and wallpaper that makes it look nice.
  • JavaScript is the electricity and plumbing that makes it work.


Here's a simple example of using HTML, CSS, and JavaScript:

h1 {
color: blue;
font-size: 20px;
function showMessage() {
alert("Hello, world!");
<h1>Welcome to my website!</h1>
<button onclick="showMessage()">Click me</button>

This code creates a web page with a blue heading that says "Welcome to my website!". When you click the button, it displays a pop-up box that says "Hello, world!".