As raised in #1256218: W3 Validation errors on rel=home, out-of-the-box Drupal 7 and Omega 7 give validation errors when tested with the W3 validator, e.g.:
The 3rd party HTML5 validator service html5.validator.nu gives the same:
The question is, what can be done to fix these problems? Is it a problem with the validators being inflexible or are the errors legit?