Unknown XML character encoding: foo

There is a problem with the character encoding specified at the start of this XML document. This may be a typo, a form other than the preferred one (for example, utf_8 rather than utf-8), or just an encoding that the validator cannot deal with.

Correct the declaration, re-encode the document with an encoding such as UTF-8 or UTF-16 or report the omission if this is a registered character set.