Should HTML meta charset be lowercase or uppercase?

Normally UTF should be uppercased as it's an abbreviation. However, attributes in HTML are normally lowercased.

So, should it be: <meta charset="UTF-8"/> or <meta charset="utf-8"/>?
I know both work.

Thank you.

The value for charset is case-insensitive.

From spec.whatwg.org > The charset attribute specifies the character encoding used by the document. This is a character encoding declaration. If the attribute is present, its value must be an ASCII case-insensitive match for the string "utf-8".

Link to full document: https://html.spec.whatwg.org/multipage/semantics.html#attr-meta-charset

As per the W3C: > A case-insensitive match for any character set name for which the IANA [Character Sets] registry has a Name or Alias field labeled as “preferred MIME name”; or, if none of the Alias fields are so labeled, a case-insensitive match for a Name field in the registry.

The specification does not specifically provide for a canonical case. Previously, I would have suggested you just use UTF-8 (from the registry), however the world is moving to lowercase and I now prefer utf-8 as it aligns better with all your other HTML.