Validator.nu Form Upload Input
To use Validator.nu as a Web service by form-based file upload, the client issues an HTTP request either to
http://html5.validator.nu/ using the POST method with an
multipart/form-data entity body. Common parameters are encoded as form fields. The document to check is included as the value of a file upload field called
file field must be the last field in the submission.
The parameter field values must decode as UTF-8.