HTML Vs. XHTML: Key Differences & Usages Explained with Examples

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When you open a website or click on a webpage, what you're actually seeing is the result of a markup language working behind the scenes. The structure and format of content on the web are arranged using markup languages, ensuring everything looks and behaves the way it should. One of the most common comparisons in web development is between HTML and XHTML. While they may look similar on the surface, they follow different rules and serve slightly different purposes. In this article, we’ll explore the difference between HTML and XHTML. 

We’ll walk you through their definitions, uses, key differences, and pros and cons—so by the end, you’ll know exactly which one suits your needs or why the distinction matters in modern web design.

A Brief Overview of HTML & XHTML

HTML

HTML (HyperText Markup Language) is the standard language used to create and structure content on the web. It was developed by Tim Berners-Lee in the early 1990s and has evolved over time, with HTML5 being the latest major version.

XHTML

XHTML (eXtensible HyperText Markup Language) is a stricter, XML-based version of HTML. It was developed by the W3C as a way to bring the rigorous syntax rules of XML into web development.

Unlike traditional HTML, XHTML enforces proper tag nesting, case sensitivity, and the closing of all elements. It’s designed for better consistency, compatibility with XML tools, and improved data handling across platforms.

Key Differences Between HTML and XHTML

Evolution of HTML

The original purpose of HTML was to facilitate the sharing and linking of documents through hypertext. Early versions were very simple, focusing primarily on structuring basic text, adding links, and embedding images.

Over time, HTML evolved through several versions to support the increasing demands of web design and interactivity. HTML 2.0 was standardized in 1995, introducing form elements, tables, and basic formatting capabilities. HTML 3.2 and HTML 4.01, released in the late 1990s, expanded the language significantly, adding support for scripting (via JavaScript), styling (via CSS), and more complex layouts.

In the early 2000s, XHTML emerged as a reformulation of HTML using XML syntax, aiming to enforce stricter coding practices. However, due to its rigidity and compatibility issues, its adoption was limited.

The most significant leap came with HTML5, officially finalized in 2014. HTML5 introduced powerful features like native audio and video support, semantic elements, offline storage, canvas for drawing, and APIs for geolocation and drag-and-drop functionality. It marked a major shift toward building more dynamic, app-like experiences directly in the browser.

Today, HTML5 continues to be the backbone of web development, evolving through community-driven updates to support the ever-changing landscape of web technologies.

Features of HTML

HTML defines the layout of web pages by using a system of tags and elements to embed text, images, links, forms, multimedia, and other components within browsers.

Let us take a look at some of the key features that define HTML:

• Markup-Based: HTML is not a programming language but a markup language that uses a predefined set of tags to instruct the browser on how to display content.
• Structure and Layout: It helps in organizing web content into a structured format using elements like headings, paragraphs, lists, tables, sections, and divisions.
• Hyperlinking: One of the core features of HTML is the ability to link pages using the <a> tag, enabling seamless navigation between documents or websites.
• Media Integration: HTML allows the embedding of images, audio, video, and other multimedia content directly into a web page using tags like <img>, <audio>, and <video>.
• Form Handling: With elements like <form>, <input>, <select>, and <textarea>, HTML provides the foundation for collecting user input in web applications.
• Semantic Elements: Modern HTML (HTML5) includes semantic tags like <article>, <section>, <nav>, and <footer> that enhance readability and improve SEO by conveying the meaning of content blocks.
• Cross-Platform Compatibility: HTML works across all major browsers and devices, ensuring that web pages can be viewed and accessed universally.
• Foundation of the Web: Along with CSS and JavaScript, HTML forms the core technology stack of web development.

Coding Rules in HTML

HTML Documents

All HTML documents must start with a document type declaration: <!DOCTYPE html>.

The HTML document itself begins with <html> and ends with </html>.

The visible part of the HTML document is between <body> and </body>.

The <!DOCTYPE> Declaration

The <!DOCTYPE> declaration represents the document type and helps browsers display web pages correctly.

It must only appear once, at the top of the page (before any HTML tags).

The <!DOCTYPE> declaration is not case sensitive.

HTML Headings

HTML headings are defined with the <h1> to <h6> tags.

<h1> defines the most important heading. <h6> defines the least important heading.

HTML Paragraphs

HTML paragraphs are defined with the <p> tag.

HTML Links

HTML links are defined with the <a> tag.

HTML Images

HTML images are defined with the <img> tag. The source file (src), alternative text (alt), width, and height are provided as attributes.

Advantages & Disadvantages of HTML

Evolution of XHTML

XHTML (Extensible HyperText Markup Language) was introduced in 2000 by the W3C as a response to the growing need for more rigorous and well-structured web documents. It emerged from HTML 4.01, combining the widely adopted features of HTML with the strict syntax rules of XML. The primary goal of XHTML was to bring more discipline to web development and to ensure better compatibility across devices and platforms.

The initial version, XHTML 1.0, retained the same elements and attributes as HTML 4.01 but required developers to write well-formed, case-sensitive markup with all tags properly closed and nested. This strictness aimed to promote clean coding practices and enable easier integration with other XML-based technologies. XHTML 1.0 was released in three document types: Strict, Transitional, and Frameset, offering varying levels of flexibility for developers.

Following that, XHTML 1.1 was introduced in 2001, further modularizing the language to allow custom profiles tailored to specific device requirements, especially for mobile and embedded systems. However, despite its technical advantages, XHTML adoption remained limited, largely due to its incompatibility with legacy HTML browsers when served with the application/xhtml+xml MIME type.

Attempts to standardize XHTML 2.0, which aimed to depart more significantly from HTML in favor of a cleaner and more extensible model, were ultimately discontinued in 2009 due to a lack of widespread support and overlap with the rapidly evolving HTML5 specification.

With the success and flexibility of HTML5, XHTML has gradually taken a backseat in mainstream web development. However, its legacy lives on through strict coding conventions and XML-compatible web applications.

XHTML is still used in specialized domains where well-formed markup and strict validation are critical, such as in embedded systems, scientific publishing, and content syndication via XML-based protocols. Today, while HTML5 dominates the landscape, XHTML remains relevant for developers and organizations that require the precision and extensibility offered by XML standards.

Features of XHTML

XHTML (Extensible HyperText Markup Language) is a reformulation of HTML using the syntax rules of XML (Extensible Markup Language). It aims to combine the strengths of HTML and XML by providing a stricter, more standardized approach to writing web content. XHTML documents must be well-formed and follow more rigid rules than traditional HTML, making them ideal for platforms that demand consistency and extensibility.

Let us look at some of the key features of XHTML: 

XML-Based Syntax: XHTML is an application of XML, which means all tags must be properly closed, nested, and written in lowercase. This ensures consistency and machine-readability across various platforms.

Stricter Rules: Unlike HTML, XHTML enforces a more disciplined structure. Tags must be closed (e.g., <br />, <img />), attributes must be quoted, and tag nesting must be correct, reducing the chances of malformed documents.

Improved Compatibility: Because XHTML follows XML standards, it allows for better integration with other XML-based languages and technologies, making it more suitable for cross-platform data sharing and device-independent applications.

Well-Formed Documents: A key feature of XHTML is its requirement for well-formed documents, which ensures that every element is properly nested and closed, enhancing document reliability and reducing rendering inconsistencies.

Transitional and Strict Versions: XHTML comes in different flavors, such as XHTML 1.0 Transitional (allowing some deprecated HTML elements) and XHTML 1.0 Strict (enforcing stricter standards). This gives developers flexibility during the transition from HTML.

Backward Compatibility with HTML: XHTML was designed to be compatible with existing HTML browsers, provided that documents are served with the correct MIME type (application/xhtml+xml or text/html).

Better Error Handling: Since XHTML adheres to XML rules, errors are not tolerated as they might be in HTML. This strictness helps catch bugs early in development and enforces cleaner, more maintainable code.

Extensibility: As it is based on XML, XHTML can be easily extended with custom tags and elements, making it a future-proof choice for scalable and modular web applications.

Coding Rules in XHTML

DOCTYPE Declaration

All XHTML documents must have a DOCTYPE declaration at the start. There are three types of DOCTYPE declarations, which are discussed in detail in the XHTML Doctypes chapter.

Case Sensitivity

XHTML is a case-sensitive markup language. All the XHTML tags and attributes need to be written in lowercase only.

Closing the Tags

Each and every XHTML tag should have an equivalent closing tag; even empty elements should have closing tags.

Attribute Quotes

All the values of XHTML attributes must be quoted. Otherwise, your XHTML document is assumed to be an invalid document.

Attribute Minimization

XHTML does not allow attribute minimization. It means you need to state the attribute and its value explicitly.

The Most Important Differences from HTML

• <!DOCTYPE> is mandatory
• The xmlns attribute in <html> is mandatory
• <html>, <head>, <title>, and <body> are mandatory
• Elements must always be properly nested
• Elements must always be closed
• Elements must always be in lowercase
• Attribute names must always be in lowercase
• Attribute values must always be quoted
• Attribute minimization is forbidden

Advantages & Disadvantages of XHTML

Similarities Between HTML and XHTML

In contrast to the differences between HTML and XHTML, there are several points of similarity between the two:

• Tag-based Structure: Both HTML and XHTML use tags to define the structure and elements of web pages, such as headings, paragraphs, lists, links, and tables.
  
  
• Core Elements and Attributes: They share the same set of core elements (like <html>, <head>, <body>, <p>, <a>, etc.) and attributes, ensuring that content structured in either language appears similarly in browsers.
  
  
• Browser Rendering: Most modern web browsers render HTML and XHTML pages in the same way, making them visually indistinguishable under normal conditions.
  
  
• Web Development Purpose: Both serve the same fundamental purpose—to structure and present content on the World Wide Web.
  
  
• W3C Standards: HTML and XHTML are both maintained and standardized by the World Wide Web Consortium (W3C).
  
  
• Support for CSS and JavaScript: Both languages support the integration of CSS for styling and JavaScript for scripting to enhance interactivity.
  
  
• Hypertext Capabilities: They both support hyperlinking using the <a> tag, allowing for navigation between documents and websites.
  
  
• Media Embedding: Both HTML and XHTML can embed media like images (<img>), videos (<video>), and audio (<audio>) into web pages.
  
  
• Forms and User Input: They provide similar elements (<form>, <input>, <textarea>, etc.) for creating forms and capturing user input.

Key Difference Between HTML and XHTML Explained

In this section, we will elaborate on a few key differences between HTML Vs. XHTML:

Syntax Variations

HTML is more lenient with its syntax. For example, in HTML, it’s acceptable to leave some tags open (like <br> or <img>), use uppercase tag names, or skip quotation marks around attribute values. This flexibility makes HTML easier to write, but can lead to inconsistencies. XHTML, on the other hand, is much stricter. It is based on XML rules, which require:

• Proper nesting of elements
  
• Lowercase tag names
  
• All tags to be closed (either with a closing tag or self-closing like <br />)
  
• Attributes enclosed in quotation marks

These rules ensure well-formed documents but demand more discipline from the developer.

HTML and XHTML Specifications

HTML is governed by the W3C and WHATWG specifications and has evolved into HTML5, which is the current standard for web development. It is designed to be forgiving of errors and is more flexible for developers.

XHTML is a reformulation of HTML using XML (Extensible Markup Language). It was created to enforce stricter standards and facilitate easier parsing by XML tools. It follows the rules defined by XML 1.0 and was originally intended to promote cleaner, more structured code.

Compatibility with Different Browsers

HTML enjoys broader browser support and is more forgiving of syntax errors. Browsers are designed to render HTML even when the markup isn’t perfectly written, which enhances compatibility and user experience.

XHTML is less forgiving. If a browser encounters a single error in XHTML code, especially when served with an XML MIME type (application/xhtml+xml), it may stop rendering the page entirely. This strictness can cause compatibility issues, especially in older or non-compliant browsers.

Uses of HTML vs. XHTML

HTML is widely used for general web development across all kinds of websites and applications. It is the preferred choice due to its flexibility, compatibility, and ease of use.

XHTML is typically used in environments where strict data formatting is essential or where XML tools need to parse content reliably. It’s also used in web applications that demand interoperability with XML-based systems, such as data exchange between services.

Rules in HTML & XHTML

Closure of Elements

HTML: Closing tags are sometimes optional. For instance, <li>, <br>, or <p> elements can be left open in HTML, and browsers will attempt to render them correctly.

XHTML: All elements must be properly closed. For example, <br> becomes <br />, and every <p> must have a closing </p>.

Nesting Elements

HTML: Tag nesting can be inconsistent and still render fine. Browsers are designed to be forgiving and auto-correct malformed markup.

XHTML: Tags must be properly nested. For example, <b><i>Text</b></i> is invalid in XHTML. The correct version would be <b><i>Text</i></b>.

An XHTML Document with a Minimum of Required Tags

A minimal valid XHTML document must include:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
<title>Example</title>
  </head>
  <body>
<p>Hello World</p>
  </body>
</html>

Empty Elements

HTML: Empty elements like <br>, <img>, or <hr> are allowed without a closing slash.

XHTML: These elements must be self-closed, for example: <br />, <img src="..." alt="..." />, <hr />.

Attribute Names

HTML: Attribute names are not case-sensitive. Both <input TYPE="text"> and <input type="text"> work.

XHTML: All attribute names must be lowercase, for XML compliance, e.g., <input type="text" />.

Attribute Minimization

HTML: Allows attribute minimization. For example, <input disabled> is valid.

XHTML: Does not allow attribute minimization. You must write the full attribute-value pair: <input disabled="disabled" />.

Document Type Declaration

HTML: Modern HTML5 uses a simplified declaration: <!DOCTYPE html>

XHTML: Requires a complete and specific DOCTYPE to validate properly: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

Case Sensitivity

HTML: Tag names and attribute names are case-insensitive.

XHTML: Everything is case-sensitive. All tag and attribute names must be lowercase.

Quoting Attribute Values

HTML: Quoting attribute values is recommended but not mandatory (e.g., <input type=text> works).

XHTML: All attribute values must be enclosed in quotes (e.g., <input type="text" />).

Conclusion

Both HTML and XHTML serve as essential building blocks for creating web pages, but they differ significantly in structure, rules, and usage. HTML is more forgiving in terms of syntax, making it easier for beginners and widely supported across browsers, while XHTML enforces stricter coding standards due to its XML-based syntax, ensuring cleaner and more consistent code.

Choosing between HTML and XHTML depends on the nature of the web project. For projects requiring compatibility, flexibility, and ease of development, HTML is often preferred. On the other hand, XHTML is suitable when a strict document structure and XML tool integration are important. Understanding the differences between HTML and XHTML helps developers adopt the most appropriate approach for their needs, ensuring both functionality and maintainability in web development.

Frequently Asked Questions (FAQs)

1. What's the main difference between HTML and XHTML?

The core difference is that XHTML is a stricter, XML-based version of HTML. Think of it this way: HTML is more forgiving with syntax errors, while XHTML demands perfectly formed, well-structured code that adheres to XML rules.

2. Why was XHTML created?

XHTML was developed to bridge the gap between HTML and XML. Its aim was to combine HTML's widespread use for web pages with XML's strict, extensible, and machine-readable nature. The idea was to create a more robust, parsable language that would be easier for browsers and other tools to process, especially with the rise of different devices and data exchange.

3. What are some key syntax differences?

XHTML imposes several strict rules that HTML doesn't always require:

• Lowercase Tags: All element and attribute names must be in lowercase.
• Closing Tags: Every opening tag must have a corresponding closing tag. Empty tags must also be self-closed.
• Attribute Values in Quotes: All attribute values must be enclosed in quotes.
• No Attribute Minimization: Attributes must have a value.
• Root Element: Every XHTML document must have a single root element. 
• Proper Nesting: Elements must be properly nested.

4. Is XHTML still relevant today?

Not really, in most modern web development. While it had its moment, the web has largely moved past XHTML. HTML5, with its new features, improved semantics, and backward compatibility, became the dominant standard. Browsers treat most XHTML documents as HTML, so the strictness often doesn't provide the intended benefits in practice anymore.

5. Why did HTML5 supersede XHTML?

HTML5 was developed to be more flexible and practical. It introduced new functionalities (like native video and audio), better semantic elements, and simplified parsing rules. Unlike XHTML's strictness, HTML5 embraced a more robust error-handling approach, making it easier for developers and more compatible across various browsers and devices without requiring perfect XML parsing. It focused on actual web needs rather than strict XML compliance.

6. Do modern browsers support XHTML?

Yes, modern browsers technically support XHTML, but they typically render it in "quirks mode" or treat it as HTML, largely ignoring the strict XML parsing rules. This means that if you serve an XHTML document with an application/xhtml+xml MIME type (which is necessary for true XHTML parsing), older versions of Internet Explorer might prompt to download the file, and syntax errors would break the page entirely. Due to these complexities and the benefits of HTML5, true XHTML parsing is rarely used or expected.

This article was contributed by Johns Joseph, Unstop Intern and Campus Ambassador.

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