HTML Validator - This interface to HTML5 document checking is deprecated.

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This interface to HTML5 document checking is deprecated.
https://forums.adobe.com/thread/1865277

https://validator.w3.org/
This interface to HTML5 document checking is deprecated.
Use the Nu Html Checker at https://validator.w3.org/nu/ directly instead.

brackets-w3cvalidation の対応が早かった。
https://github.com/cfjedimaster/brackets-w3cvalidation
https://github.com/cfjedimaster/brackets-w3cvalidation/commit/fc8b38d13be191ec4da44dfe4a344cc2218c971d