; header fields
[
  (header_field_email)
  (header_field_subject)
  (header_field)
] @keyword

(header_separator) @punctuation.delimiter

(header_subject
  (header_unstructured) @markup.heading)
(header_other
  (header_unstructured) @comment)

(atom) @variable

(email) @string

; (header_subject) @markup.heading
; (header_other) @markup.environment