===============
@ in keys
===============

@article{f@oo,}

---

(program (entry (name) (key)))

===============
@ in identifiers
===============

@article{foo,
au@thor="me"
}

---

(program
  (entry (name) (key)
    (field (identifier) (value (string (text))))))

===============
@ in string macros
===============

@string{!@&*="this"}

@article{foo,
au@thor=!@&*
}

---

(program
  (string_command (name)
    (identifier) (value (string (text))))
  (entry (name) (key)
    (field (identifier) (value (identifier)))))