XHTML, which stands for Extensible HyperText Markup Language, is a reformulation of HTML (HyperText Markup Language) as an XML (Extensible Markup Language) application. Here’s a brief overview:

Key Characteristics:

  1. Combination of HTML and XML: XHTML was developed to make HTML more extensible and to increase its interoperability with other data formats.
  2. Stricter than HTML: While HTML is lenient in its syntax, allowing browsers to interpret and display poorly structured documents, XHTML is more strict, enforcing well-formedness rules of XML.

Differences from HTML:

  1. Document Structure: XHTML documents must be well-formed, meaning they follow the specific structure and rules of XML.
  2. Case Sensitivity: Element and attribute names in XHTML must be in lowercase.
  3. Closing Tags: All elements in XHTML must have a closing tag or be self-closed. For instance, the line break in HTML (<br>) would be written as <br /> in XHTML.
  4. Attribute Values: All attribute values must be enclosed in quotes.
  5. Nested Elements: Elements must be properly nested and not overlap.

Versions:

  1. XHTML 1.0: This was the first specification of XHTML, and it was essentially a reformulation of HTML 4.01 using XML rules. It came in three doctypes: Strict, Transitional, and Frameset.
  2. XHTML 1.1: Introduced as a modularized version, allowing developers to create custom document types by combining different modules.
  3. XHTML5: With the development of HTML5, the term “XHTML5” refers to the XML-serialized version of HTML5.

Why XHTML?

  • Consistency: XHTML’s strict rules ensure a consistent structure, which can be beneficial when using automated tools or parsers.
  • Future-Proofing: XHTML was seen as a way to ensure that documents would remain compatible with future versions of HTML or other XML-based languages.
  • Interoperability: As an XML application, XHTML can work more seamlessly with other XML data formats.

Current Status:

XHTML’s significance has waned with the advent and wide adoption of HTML5. While XHTML brought many benefits, many developers found its strictness cumbersome. HTML5 offers many of the advanced features that developers wanted, but without the strict syntax rules of XHTML. As a result, while XHTML is still supported, HTML5 is the recommended standard for web development as of now.