On the MWG page (https://exiftool.org/TagNames/MWG.html), there's a link to Archive.org for the specs. That link only shows the page where the specs could have been downloaded, but you can't actually download the PDF from there, as the download links point to the original MetadataWorkingGroup.org website.
I suggest instead linking directly to the pdf
https://web.archive.org/web/20180919181934/http://www.metadataworkinggroup.org/pdf/mwg_guidance.pdf
Done. Thanks.
- Phil