Developer 

How to shape and extend the JSON output. Each topic has its own page:

• cObjects — the headless TypoScript content objects: JSON, CONTENT_JSON, plus the casting objects BOOL/INT/FLOAT.
• Custom content — custom content elements, internal Extbase plugins, integrating external plugins (EXT:news et al.), custom TypoScript objects and meta-data overrides.
• Data processors — DatabaseQueryProcessor, FilesProcessor, MenuProcessor, GalleryProcessor and friends, with their headless-specific options.
• Events — PSR-14 extension points and how to register listeners; full list in Reference: Events.
• Images & files — file/image payloads and processing configuration (the storage proxy itself is a feature flag, see Configuration).
• Snippets — drop-in recipes for common tasks.

Form output decorators are documented with the rest of the form integration in EXT:form; the default response shape and every shipped lib.* object in Reference: TypoScript helpers.