Field keys

Three key formats, one mental model — external (position), internal (id), and definition.

Content coming soon. Outline the field-key patterns:

Flat — email
Group child — address.street
Simple array — phones[0] (external) / phones[_0] (internal)
Group array child — addresses[0].street (external) / addresses[_0].street (internal)
Definition key — phones (the array itself)

Single-level nesting only: address.street is fine, address.location.street is not.