Support both '@id/id' and '@type/type'

[thill-odi]

Because inclusion of the '@' symbol played havoc with so many systems, OpenActive standards originally truncated JSON-LD's '@type' and '@id' attributes to simply 'type' and 'id'.

With increasing awareness of, and conformance with, JSON-LD, however, publishers are increasingly adopting the '@type' and '@id' forms by default. All harvester and related tooling should therefore be capable of parsing both:

• 'id' and '@id'
• 'type' and '@type'.