I have tried to use the HTML5 validator.
In my pages I use the charset tag:
and know that I am using specifik danish 8859-1 characters in my pages.
The validator returns the error text:
"Internal encoding declaration iso-8859-1 disagrees with the actual encoding of the document (utf-8).."
In my opinion the validator should check if the charset-metatag i syntactically correct and when so validate the page on this basis without making its own decisions or questioning my choise of charset.
In fact I do require to use iso-8859-1 on my pages and expects consequently to be told if there are any errors in my pages on this basis.