dataKey property
Dotted path to the payload, resolved from the root of the body.
'data' selects one level, 'data.items' two, 'data.pages[0].items'
indexes a list, and r'meta.user\.name' escapes a literal dot. Empty —
the default — means the body itself.
Resolved relative to the deprecated nestedKey while that is still set.
Implementation
final String dataKey;