A file upload field.
Your form must not have an
enctype="multipart/form-data" attribute as these elements do not use
Files are uploaded immediately the user selects them, and the form is submitted only after they have finished uploading. The submitted form data only includes the digest of the file. This allows file fields to be part of the normal form handling, including validation.
When re-rendering a form, a secret is included, to prevent users accessing a given file where they know a digest.
When rendering a document, the download links have authentication signatures.
A single file upload field just presents an ‘Upload file…’ link. See also File repeating section for uploading multiple files and enabling full drag and drop file uploads.
All the common properties are supported.