https://pdf.metadata.care/help/xmp-metadata/
XMP metadata in PDF files | Pdf Metadata Editor
Overview of the avaiable XMP metadata types
xmp metadatain pdffileseditor
https://mail.kde.org/pipermail/digikam-devel/2013-September/069284.html
[Digikam-devel] [digikam] [Bug 324375] XMP Metadata tab shows "Label" set by VIewNX, but Filter...
https://mail.kde.org/pipermail/digikam-devel/2014-June/072743.html
[Digikam-devel] [digikam] [Bug 336328] Tags Manager's Sync Export DB to metadata, mirrors XMP but...
https://www.iso.org/standard/79384.html
ISO 16684-3:2021 - Graphic technology — Extensible metadata platform (XMP) specification — Part 3:...
Graphic technology — Extensible metadata platform (XMP) specification — Part 3: JSON-LD serialization of XMP
https://www.iso.org/standard/75163.html
ISO 16684-1:2019 - Graphic technology — Extensible metadata platform (XMP) — Part 1: Data model,...
Graphic technology — Extensible metadata platform (XMP) — Part 1: Data model, serialization and core properties
https://groups.oasis-open.org/communities/community-home/digestviewer/viewthread?GroupId=205&MessageKey=2a2d0e87-82fa-4003-a7e3-8893667a2eb8&CommunityKey=4bf06d41-79ad-4c58-9e8e-018dc7d05da8&hlmlt=VT
RE: [office] XMP XML:RDF Metadata | OASIS Open Document Format for Office Applications...
open document format
https://www.iso.org/standard/57421.html
ISO 16684-1:2012 - Graphic technology — Extensible metadata platform (XMP) specification — Part 1:...
Graphic technology — Extensible metadata platform (XMP) specification — Part 1: Data model, serialization and core properties