This validation error shows for all pages with an edit link. As noted, the "edit" keyword is not registered with the W3C.
This can easily be fixed by adding the keyword:
This needs to be evaluated by a developed, and if it is determined that registration is the fix, then a developer should do this to ensure that the proper descriptions are added.
See also Bug 40384, which would have a similar fix.
HTML validation is important. When editors manually create HTML ids, such as
certain citation templates, we recommend they validate the page to ensure they
have no duplicates. They get bogged down in endemic validation errors.