Web Hypertext Application Technology Working Group (WHATWG)
WHATWG, the Web Hypertext Application Technology Working Group, is a community that develops and maintains web standards, including the HTML Living Standard, DOM, Fetch, URL, and Streams specifications.
WHATWG was founded in 2004 by Apple, Mozilla, and Opera in response to the W3C’s direction. It introduced the concept of a living standard: a continuously updated specification with no versioned releases.
PHP developers encounter WHATWG specifications when implementing URL parsing compliant with the WHATWG URL Standard, HTML sanitation, stream handling, or building server-side applications that must align with browser behavior.