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●About W3C
  
https://html.spec.whatwg.org/multipage/  is the current HTML standard. It obsoletes all other  previously-published HTML specifications.  
As announced at  https://www.w3.org/blog/2019/05/w3c-and-whatwg-to-work-together-to-advance-the-open-web-platform/,  the W3C and the WHATWG signed an agreement to collaborate on the  development of a single version of the HTML and DOM specifications:  

● https://html.spec.whatwg.org/multipage/  is the single version of HTML being actively developed  
●https://dom.spec.whatwg.org/  is the single version of the DOM specification being actively  developed.  
For further details about the W3C-WHATWG agreement, see the  Memorandum of Understanding Between W3C and WHATWG.