The W3C Extensible Hypertext Markup Language (extensible HTML; XHTML) is a text-based markup language for structuring and semantically marking up content such as text, images and hyperlinks in documents. It is mostly a reformulation of HTML 4.0 in XML. In contrast to HTML, which was defined using SGML, XHTML uses the stricter and easier to parse SGML subset XML as the language basis. XHTML documents therefore satisfy the syntax rules of XML.
XHTML serves as a bridge between HTML and XML. Its inception aimed to combine the best of both worlds: the structure and presentation capabilities of HTML with the strict syntax and extensibility of XML.
While HTML, prior to HTML5, was defined as an application of Standard Generalized Markup Language (SGML), a flexible markup language framework, XHTML is an application of XML, a more restrictive subset of SGML. XHTML documents are well-formed and may therefore be parsed using standard XML parsers, unlike HTML, which requires a lenient HTML-specific parser. XHTML 1.0 became a World Wide Web Consortium (W3C) recommendation on 26 January 2000. XHTML 1.1 became a W3C recommendation on 31 May 2001. XHTML is now referred to as “the XML syntax for HTML” and being developed as an XML adaptation of the HTML living standard.
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What is XHTML5?
XHTML5 is simply XML-serialized HTML5 data (HTML5 constrained to XHTML’s strict requirements such as not having any unclosed tags). HTML that has been written to conform to both the HTML and XHTML specifications and therefore produces the same DOM tree whether parsed as HTML or XML is known as polyglot markup.
Newer XHTML document types no longer include layout markups. XHTML Transitional 1.0 is the last document type that still contains layout elements. In more modern document types, there are still few layout elements, but only for reasons of backward compatibility with the transitional document types. Finally, in XHTML Basic or XHTML 2, layout elements are no longer included at all. For the visual design of XHTML elements, only external CSS rules should be referenced.
In order to enable the development of languages based on XHTML, related and related elements have been grouped together in XHTML 1.1 in so-called modules. Based on these modules, which are written in DTDs and in the future in XML Schema, you can compile your own XHTML document types according to the modular principle and mix them with other XML-based languages. Example applications of XHTML modularization are XHTML 1.1, XHTML Basic, and the blends with SMIL (multimedia), SVG (vector graphics), and MathML (mathematical formula set). For the integration of general objects such as multimedia plug-ins, there is the object module.
XHTML5 provides benefits such as improved compatibility with XML tools and parsers, cleaner code structure, better support for modern web development practices, and enhanced accessibility features. However, it’s worth noting that HTML5 has gained wider adoption in recent years due to its flexibility and compatibility with a broader range of web development tools and frameworks.
Key Features of XHTML
- Compatibility with XML: One of the defining features of XHTML is its compatibility with XML. This allows XHTML documents to be parsed and manipulated using XML tools and libraries, opening up possibilities for more sophisticated processing and transformation.
- Strict Syntax Rules: XHTML enforces stricter syntax rules compared to HTML. This includes requirements such as properly nested elements, lowercase tag names, and attribute values enclosed in quotes. These rules promote consistency and interoperability across different platforms and devices.
- Modularity and Extensibility: Like XML, XHTML supports modularity and extensibility through the use of namespaces and custom elements. This enables developers to define their own elements and attributes, facilitating the creation of specialized vocabularies for specific purposes.
- Accessibility and Device Independence: By adhering to XHTML’s strict syntax and semantics, developers can create web pages that are more accessible and device-independent. This means content can be rendered correctly across a wide range of devices, including desktop computers, smartphones, and assistive technologies.
Use Cases of XHTML5
XHTML serves as an excellent choice for data interchange formats, especially in scenarios where structured data needs to be exchanged between different systems or platforms. Its XML-based syntax ensures that data remains well-formed and easily parsable by XML processors, making it suitable for applications such as web services, APIs, and data feeds.
In specialized applications where XML processing is prevalent, such as content management systems (CMS), document management systems (DMS), and e-publishing platforms, XHTML provides a standardized and interoperable markup language for representing content. Its strict syntax rules and compatibility with XML tools make it well-suited for managing and manipulating structured data.
XHTML’s adherence to strict syntax and semantics promotes accessibility and device independence, making it an ideal choice for creating web content that needs to be accessible to users with disabilities or rendered correctly across different devices and platforms. Government websites, educational portals, and corporate intranets often leverage XHTML to ensure compliance with accessibility standards and reach a diverse audience.
XHTML encourages semantic markup practices by providing a standardized set of elements and attributes for representing content. By using meaningful element names and attribute values, developers can enhance the structure and meaning of their documents, improving search engine optimization (SEO), accessibility, and content reusability.
In environments where legacy systems or applications rely on XML-based data formats, XHTML can serve as a bridge for integrating new web technologies with existing infrastructure. By leveraging XHTML’s compatibility with XML, developers can facilitate data exchange and interoperability between modern web applications and legacy systems without the need for extensive modifications.
XHTML is often used in documentation and standards compliance efforts, particularly in industries where strict adherence to markup standards is required, such as healthcare, finance, and government. By using XHTML to author documentation and technical specifications, organizations can ensure consistency, interoperability, and compliance with industry standards and regulations.
XHTML’s support for Unicode and internationalization features makes it suitable for creating multilingual web content that can be easily localized and translated into different languages. Websites, applications, and online platforms targeting global audiences often rely on XHTML to manage and present multilingual content in a standardized and interoperable manner.
Code Examples of XHTML
An example of how a registration for a chat could be realized. The chat corner can also be on a different computer than the form. In this way, the chat corner can be shared. For example, a hidden input that the utility evaluates could be used to dynamically adapt the display of the chat corner to the page from which the login is made.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | <form action="http://example.org/chat-login.php" method="post"> <fieldset> <legend>Register for the chat session</legend> <ul> <li><label for="nickname">Nickname:</label> <input type="text" id="nickname" name="nickname" /></li> <li><label for="password">Password:</label> <input type="password" id="password" name="password" /></li> <li>Status:<br /> <label for="withMagic Wand">With Magic Wand</label> <input type="radio" id="withMagic Wand" name="status" value="with" /><br /> <label for="withoutmagicwand">Without magicwand</label> <input type="radio" id="withoutMagic Wand" name="status" value="without" checked="checked" /> </li> <li><input type="submit" value="White Cat, Golden Cat, Polka Dot Cat - and I'm here!" /> <input type="hidden" name="cat_tail" value="cat tail div" /> </li> </ul> </fieldset> </form> |
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Untitled by Abhishek Ghosh (@abhishekghosh-the-encoder)
on CodePen.
This is another example, this is from javascriptkit.com.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <title> Strict DTD XHTML Example </title> </head> <body> <p> Please Choose a Day: <br /><br /> <select name="day"> <option selected="selected">Monday</option> <option>Tuesday</option> <option>Wednesday</option> </select> </p> </body> </html> |
See the Pen
Untitled by Abhishek Ghosh (@abhishekghosh-the-encoder)
on CodePen.
In summary, XHTML offers a versatile and standardized approach to creating structured, interoperable, and accessible web content across various domains and industries. Its compatibility with XML, coupled with its support for semantic markup and accessibility features, makes it a valuable tool for data interchange, specialized applications, standards compliance, and multilingual content management.
