XHTML and HTML Relationship and Differences

XHTML is built on top of HTML, with the goal of making HTML more robust and flexible.

XHTML documents are written in XML syntax, which requires every element to be properly closed. This is in contrast to HTML, where elements can be left open.

XHTML is designed to be more strict and consistent than HTML, with a focus on separating presentation and structure.

XHTML is the next generation of HTML, and it's designed to be used with XML. It's a new technology that's rapidly evolving, with the W3C issuing the recommendation for version 1.0 on January 26, 2000.

One of the key differences between HTML and XHTML is that XHTML is a strict language, unlike HTML which is loose and forgiving. This means that XHTML demands firm adherence to the rules of grammar, making it a bit more challenging to work with.

XHTML is derived directly from HTML version 4.01, and it's designed to be used with XML. This is part of a whole new suite of "X" technologies, including XML, XPATH, XSL, and XSLT, that are destined to have a profound effect on the Internet.

XHTML is a user-friendly language, and its syntax and coding rules are very straightforward and easy to implement. The rules are designed to allow a seamless integration of XHTML with XML and other related "X" technologies.

Here are the fundamental differences between HTML and XHTML that you need to know:

XHTML is an extension of HTML, and it's also based on the XML language. This means that XHTML has stricter guidelines than HTML, requiring a standard XML parser to read the code.

HTML, on the other hand, has a more flexible framework that can be parsed with a lenient HTML-specific parser.

Here's a comparison of HTML and XHTML in a table format:

As you can see, XHTML is a more structured and strict version of HTML, which is designed to create a more consistent web experience for users across different browsers and devices.

HTML is a fundamental language for developing websites, but it's not to be confused with XHTML or HTML5.

HTML stands for HyperText Markup Language, but that's not as important as understanding its purpose: to help you structure and format content on the web.

HTML is an extension of XML, making it stricter and more consistent than other languages.

You can think of HTML as a cross between HTML and XML, which is a big part of what makes it so useful.

HTML and XHTML are closely related, and understanding their relationship is key to grasping the differences between them.

HTML, or HyperText Markup Language, was proposed by Tim Berners-Lee in 1987 and is a flexible framework that requires a lenient HTML-specific parser.

XHTML, on the other hand, is a family of XML markup languages that mirror or extend versions of HTML, and was standardized as a World Wide Web Consortium Recommendation in 2000.

Here's a breakdown of the key differences between HTML and XHTML:

The stricter syntax of XHTML is designed to create a more consistent web experience for users across browsers, and enforces better development practices, leading to increased security and performance.

XHTML is an extension of both HTML and XML, making it a more robust and flexible language for creating web pages.

As a result, XHTML is often considered a more modern and superior choice to HTML, especially for complex web applications.

However, it's worth noting that HTML5 has largely replaced XHTML and is now the preferred choice for web development.

The main difference between XHTML and HTML 4 is that XHTML is an XML application, which requires certain changes in practice.

In particular, XHTML doesn't allow the same level of flexibility as HTML 4, which was based on SGML. This means that some things that were perfectly legal in HTML 4 are now no longer allowed in XHTML.

For another approach, see: Html 4

XHTML 1.0 was officially adopted as a W3C Recommendation in January 2000. This marked a significant milestone in the development of XHTML.

There are three formal Document Type Definitions (DTD) for XHTML 1.0, each corresponding to a different version of HTML 4.01. These are XHTML 1.0 Strict, XHTML 1.0 Transitional, and XHTML 1.0 Frameset.

The World Wide Web Consortium still uses XHTML 1.0 Strict as the document type for its homepage, as of November 2015. This suggests that XHTML 1.0 Strict is still a widely accepted and used standard.

Here's a brief summary of the three DTDs:

The first version of XHTML, 1.0, was published in December 1998 as a W3C Working Draft.

December 1998 saw the publication of a W3C Working Draft entitled Reformulating HTML in XML, which introduced Voyager, the codename for a new markup language based on HTML 4.

In February 1999, the specification was renamed to XHTML 1.0: The Extensible HyperText Markup Language.

By January 2000, XHTML 1.0 was officially adopted as a W3C Recommendation.

There are three formal Document Type Definitions (DTD) for XHTML 1.0, corresponding to the three different versions of HTML 4.01:

The second edition of XHTML 1.0 became a W3C Recommendation in August 2002.

In XHTML 2.0, the introduction of new features was minimal, and most of the focus was on cleaning up the syntax and making it more consistent.

XHTML 2.0 was designed to be a more robust and flexible language, with features like the ability to nest attributes.

One of the key goals of XHTML 2.0 was to simplify the language and make it easier to use, with a focus on reducing the number of optional features.

XHTML 2.0 also introduced a new way of handling forms, with the introduction of the "form" element.

The "form" element was designed to make it easier to create complex forms, and to provide a more consistent way of handling form data.

XHTML 2.0 was never widely adopted, and it ultimately failed to replace XHTML 1.1 as the standard for web development.

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Modularization provides an abstract collection of components through which XHTML can be subsetted and extended. This feature helps XHTML reach emerging platforms like mobile devices and Web-enabled televisions.

The first modular XHTML variants were XHTML 1.1 and XHTML Basic 1.0. They became available in 2001, after the initial draft became available in April 1999.

XHTML 1.1 evolved out of the Modularization of XHTML specification, released in September 1999. It effectively recreates XHTML 1.0 Strict with the addition of ruby annotation elements to support East-Asian languages.

Modularization is all about breaking down a technology into smaller, more manageable pieces. This allows for greater flexibility and customization.

The first modular XHTML variants were XHTML 1.1 and XHTML Basic 1.0, which emerged from the initial Modularization of XHTML specification.

These modules combined within XHTML 1.1 effectively recreate XHTML 1.0 Strict, with the addition of ruby annotation elements to better support East-Asian languages.

In September 1999, the W3C released the first draft of XHTML 1.1, which eventually reached Recommendation status in May 2001.

XHTML 1.1 is largely compatible with XHTML 1.0 and HTML 4, but it proved unable to gain widespread use due to limited browser support for the alternate application/xhtml+xml media type.

A second edition of XHTML 1.1 was issued in November 2010, addressing various errata and adding an XML Schema implementation not included in the original specification.

The XHTML Mobile Profile is a variant of the W3C's XHTML Basic specification, specifically designed for information appliances with limited system resources.

It was developed by the Wireless Application Protocol Forum in 2001, and later adopted by the Open Mobile Alliance (OMA) in 2002. The OMA continued to develop XHTML Mobile Profile as a component of their OMA Browsing Specification.

XHTML Mobile Profile 1.1 was finalized in 2004, adding partial support for the Scripting Module and Intrinsic Events. This version is part of v2.1 of the OMA Browsing Specification.

XHTML Mobile Profile 1.2 was finalized on 27 February 2007, expanding the capabilities of XHTML MP 1.1 with full support for the Forms Module and OMA Text Input Modes. It is part of v2.3 of the OMA Browsing Specification.

XHTML Mobile Profile 1.3 uses the XHTML Basic 1.1 document type definition, which includes the Target Module. Events in this version are updated to DOM Level 3 specifications.

Here's a brief timeline of the evolution of XHTML Mobile Profile:

XHTML is a markup language that combines the structure of XML with the functionality of HTML. It's a way to write web pages that's both human-readable and machine-readable.

XHTML documents have a root element called the document type declaration (DOCTYPE), which is required to indicate the document type and version. This is usually the first line of the document.

XHTML is a strict language, meaning that it enforces a specific set of rules and syntax, which can be helpful for ensuring consistency and accuracy in web page coding.

If this caught your attention, see: Content Type Text Html

XML is a shorthand name for Extensible Markup Language.

It was conceived as a means of regaining the power and flexibility of SGML without most of its complexity.

XML preserves most of SGML's power and richness, and yet still retains all of SGML's commonly used features.

Many of the more complex features of SGML that make authoring and design of suitable software difficult and costly have been removed from XML.

XHTML Basic is a feature-limited specification defined by the W3C for information appliances that lack system resources.

It provides a minimal feature subset sufficient for common content-authoring, and became a W3C recommendation in December 2000.

XHTML Basic 1.0 has the fewest features among all XHTML versions.

It implements the Core Modules, including Structure, Text, Hypertext, and List, as well as eight other abstract modules.

XHTML Basic 1.1 replaced the Basic Forms Module with the Forms Module and added Intrinsic Events, Presentation, and Scripting modules.

This version became a W3C recommendation on 29 July 2008 and supports additional tags and attributes from other modules.

The current version of XHTML Basic is 1.1 Second Edition, which re-implemented the language in the W3C's XML Schema language.

It also supports the lang attribute.

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A valid XHTML document is one that conforms to an XHTML specification, ensuring consistency in document code and easing processing. This is checked using the W3C Markup Validation Service.

A document must be well-formed, meaning all elements have closing tags or are written in a special form, and elements must nest properly. Overlapping elements are not allowed in SGML, but are tolerated in existing browsers.

To validate an XHTML document, a DOCTYPE declaration is used, which declares the Document Type Definition (DTD) to which the document conforms. This declaration should be placed before the root element.

Here are the key rules for a valid XHTML document:

Print is a specialized version of XHTML Basic designed for documents printed from information appliances to low-end printers.

XHTML-Print became a W3C Recommendation in September 2006, marking a significant milestone in the development of print-friendly document formats.

This specialized version of XHTML Basic is tailored to meet the needs of low-end printers, ensuring that documents printed from information appliances are rendered correctly and efficiently.

XHTML-Print's focus on low-end printers highlights the importance of document structure and validation in ensuring that printed documents look their best.

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The root element of an XHTML document is the foundation of the entire document structure. It must be html, and it needs to contain an xmlns attribute to associate it with the XHTML namespace.

The namespace URI for XHTML is http://www.w3.org/1999/xhtml. This is a crucial piece of information to ensure your document is properly validated.

The root element can also feature an xml:lang attribute to identify the document with a natural language, as seen in the example tag below.

A document that conforms to an XHTML specification is said to be valid, which assures consistency in document code and eases processing.

To be valid, a document must meet all the criteria for a strictly conforming XHTML document, which includes having an XML declaration, using a root element of html with an xmlns attribute, and including a Document Type Declaration (DOCTYPE) that declares the document type definition (DTD) to which the document conforms.

A well-formed XHTML document must have all elements properly nested and closed, and the xmlns attribute in the html element must specify the xml namespace for the document.

Here are some key requirements for document conformance:

A strictly conforming XHTML document must meet all of the above criteria, and a user agent must meet all of the following criteria to be considered conforming:

1. The user agent must parse and evaluate an XHTML document for well-formedness.

2. If the user agent claims to be a validating user agent, it must also validate documents against their referenced DTDs.

3. The user agent must recognize attributes of type ID as fragment identifiers.

4. The user agent must ignore entire attribute specifications if it encounters an attribute it does not recognize.

5. The user agent must use the default attribute value if it encounters an attribute value it does not recognize.

6. The user agent must process entity references as the characters that make up the entity reference if it encounters an entity reference for which it has processed no declaration.

7. The user agent must display the document in such a way that it is obvious to the user that normal rendering has not taken place if it encounters characters or character entity references that are recognized but not renderable.

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A conforming user agent must meet all of the following criteria. A validating user agent must validate documents against their referenced DTDs according to [XML].

To be consistent with the XML 1.0 Recommendation, a user agent must parse and evaluate an XHTML document for well-formedness. This means it must check if the document follows the rules of XML.

A user agent that encounters an element it does not recognize must process the element's content. This ensures that the user agent can still display the content of the element, even if it doesn't understand the element itself.

If a user agent encounters an attribute it does not recognize, it must ignore the entire attribute specification. This means that if a user agent doesn't understand an attribute, it will simply ignore it and move on.

User agents that encounter characters or character entity references that are recognized but not renderable may substitute another rendering that gives the same meaning. This can be useful when a user agent encounters a character that it can't display, but can still give an idea of what the character is.

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Here are some of the rules for handling white space in XHTML:

XHTML documents can be restricted to elements and attributes from the XML and XHTML 1.0 namespaces, making them strictly conforming.

This means that XHTML documents can include metadata expressed in RDF within XHTML documents, thanks to the ability to use XHTML with other namespaces.

In this case, a user agent would need to be able to parse and understand the additional metadata, which is a key aspect of user agent conformance.

Using XHTML with other namespaces is possible, but it's not strictly conforming XHTML 1.0 documents as defined in Section 3.1.

The XHTML namespace can be used with other XML namespaces as per [XMLNS], making it a flexible option for incorporating different types of metadata into documents.

To use XHTML with other namespaces, you need to follow the guidelines in Section 3.1.2, which explains how to combine XHTML with other XML namespaces.

This approach is demonstrated in the example of using XHTML 1.0 with the MathML Recommendation, where XHTML 1.0 markup is incorporated into another XML namespace.

Work by W3C is addressing ways to specify conformance for documents involving multiple namespaces, which is an area of ongoing development and improvement.

User Agent Conformance is a crucial aspect of XHTML. A conforming user agent must meet all of the following criteria.

To be consistent with the XML 1.0 Recommendation, a user agent must parse and evaluate an XHTML document for well-formedness. This means checking if the document adheres to the rules of XML.

A user agent must also validate documents against their referenced DTDs if it claims to be a validating user agent. This ensures that the document is not only well-formed but also valid according to the specified DTD.

When a user agent processes an XHTML document as generic XML, it shall only recognize attributes of type ID as fragment identifiers. This helps prevent incorrect interpretation of document structure.

If a user agent encounters an element it does not recognize, it must process the element's content. This ensures that the user agent does not ignore unknown elements, which could lead to incorrect rendering of the document.

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Here are the key user agent conformance criteria:

XHTML 1.x documents are mostly backward compatible with HTML 4 user agents when the appropriate guidelines are followed.

However, XHTML 2.0 is significantly less compatible, although this can be mitigated to some degree through the use of scripting.

In fact, XHTML 2.0 is so incompatible that it's often necessary to use JavaScript to make it work in older browsers.

XHTML 1.1 is essentially compatible with HTML 4, but HTML 4 browsers generally ignore the elements for ruby annotation.

Later XHTML 1.x modules, such as those for the role attribute, RDFa, and WAI-ARIA, degrade gracefully in a similar manner.

HTML5 and XHTML5 serializations are largely inter-compatible if adhering to the stricter XHTML5 syntax.

However, there are some cases in which XHTML will not work as valid HTML5, such as processing instructions being treated as comments in HTML.

Here are some examples of cross-compatibility issues between XHTML and HTML:

XHTML documents are lean, using less bandwidth, which reduces cost, particularly for large websites.

XHTML tags must have closing tags and are nested correctly, generating cleaner code. This makes it easier to maintain and update web pages.

All new developments will be in XML, of which XHTML is an application. This means XHTML is at the forefront of web development standards.

XHTML documents are well-formatted, well-structured, and can easily be transported to specialized web environments, such as wireless devices and Braille readers.

XHTML works in association with CSS to create web pages that can easily be updated.

Here are some key benefits of using XHTML:

Using XHTML has several benefits that make it a great choice for web development. XHTML documents are validated with standard XML tools.

One of the main advantages of XHTML is that it is easily maintainable, convertible, and editable in the long run. This is because XHTML documents are lean, using less bandwidth which reduces costs, especially for websites with thousands of pages.

XHTML documents are also well-formatted, well-formed, and can easily be transported to wireless devices, Braille readers, and other specialized web environments. This is a significant advantage for users with disabilities.

XHTML is an official standard of the W3C, making it more compatible and accurate with many browsers. This is a major advantage for web developers who want to ensure their websites work across different browsers and devices.

Here are some key benefits of XHTML:

Using HTML can lead to better development practices, as it enforces industry standards that increase security and performance.

Industry standards enforced by HTML, such as consistency across browsers, create a more consistent web experience for users.

Enforcing these standards results in a more consistent web experience for users across browsers for both design and user experience.

HTML development can also improve security, which is a major concern for web developers and users alike.

Getting Started with XHTML is relatively easy, and this post covers almost everything you need to get started using it.

The introduction of HTML5 has largely outgrown the use of XHTML, and most developers favor it over the former.

To get started with XHTML, you don't need to learn much, but it's worth noting that the strictness of XML is enforced.

Just be sure to do the research required to understand which is the best fit for you between XHTML and HTML5.