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1. 1. Attribute specific-use="local" to identify that a file on the webserver is used as supplementary material
   2. Attribute mimetype="[.ext]" to specify the file extension/filetype. Supported values can be found here: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types.
   3. Attribute xlink:href="supplement/[filename]" to specify the file
   4. Element <label>Download [filetype] file</label>

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