Desktop files: https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html
Desktop files: http://standards.freedesktop.org/desktop-entry-spec/
XMP: http://www.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/XMPSpecificationPart3.pdf
IPTC4XMP: http://xml.coverpages.org/IPTC-CoreSchema200503-ImplGuideLines3.pdf
Pango mark up: https://developer.gnome.org/pango/stable/PangoMarkupFormat.html
Thumbnails: https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html