Metadata vocabulary registry

The Rust core includes a deliberately small registry of optional metadata hints. It is not an allow-list and is never required to store, read, or query a metadata assertion. Unknown vocabulary and property strings remain valid and round-trip exactly.

Vocabulary	Exact identifier	Built-in property hints
IPTC Video Metadata Hub 1.7 JSON	https://iptc.org/std/videometadatahub/recommendation/iptc-vmhub-1.7-schema.json	title, keywords
Dublin Core elements	http://purl.org/dc/elements/1.1/	title, subject
XMP Basic	http://ns.adobe.com/xap/1.0/	CreateDate, CreatorTool
EBUCore	urn:ebu:metadata-schema:ebucore	vocabulary reference only
PostProject metadata	https://postproject.org/ns/metadata/	reserved; no native properties currently required

Definitions can expose accepted PostProject value kinds, single or repeated cardinality, a label and description, an authoritative reference, optional local validation, and aliases from mapping profiles. Applications opt in by looking up a definition and calling its validation method. Persistence does not call it automatically.

The IPTC hints record selected XMP and EBUCore spellings from the Video Metadata Hub mapping table. These aliases describe correspondence only. They do not turn PostProject into an XMP or EBUCore validator and do not claim that conversion is always lossless.

Authoritative references:

• IPTC Video Metadata Hub 1.7

• IPTC Video Metadata Hub mapping table

• Dublin Core Metadata Element Set

• Adobe XMP namespaces

• EBU Tech 3293

Application-specific namespaces

An application should use a stable namespace rooted in a domain it controls, for example https://editor.example/metadata/. It can store those assertions without registering the namespace with PostProject. A registry hint is useful only when shared labels, validation, or mappings justify maintaining one.