For about the first half century of its existence, transportation of mail via aircraft was usually categorized and sold as a separate service (airmail) from surface mail. Today it is often the case that mail service is categorized and sold according to transit time alone, with mode of transport (land, sea, air) being decided on the back end in dynamic intermodal combinations. Thus even "regular" mail may make part of its journey on an aircraft. Such "air-speeded" mail is different from nominal airmail in its branding, price, and priority of service.