Extensible HyperText Markup Language, a web standard combining HTML and XML rules.
Acronym formed in late 1990s from 'Extensible' + 'HTML' (HyperText Markup Language). Developed by W3C as a stricter, XML-compliant version of HTML. Represents the evolution of web standards toward more rigorous structure.
XHTML emerged during the web's adolescence when developers realized the need for stricter rules—like requiring all tags to be properly closed and lowercase. Though largely superseded by HTML5, XHTML taught an entire generation of web developers the discipline of clean, well-formed markup that still influences coding practices today.
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