The key of the header field. The key must be 1 to 40 characters in length, and can contain letters, digits, hyphens (-) and underscores (_). The key does not support Cookie or Host.
The value of the header field. The value must be 1 to 128 characters in length, and can contain lowercase letters, printable ASCII characters whose values are ch >= 32 && ch < 127, asterisks (*), and question marks (?). The value cannot start or end with a space.