Platform SDK: CDO for Windows 2000 |
Multi-part Content-Type headers identify multipart messages. They require that a subtype and other elements be included in the header.
Content-ID values should be different for each part where there are different levels of complexity between parts. The content-ID of each part should be different from the content-ID of the overall multipart/alternative. That is, one content-ID value will refer to the multipart/alternative entity, while one or more other content-ID values will refer to the parts inside it.
The multipart/byteranges content type is defined as a part of the HTTP message protocol. It includes two or more parts, each with its own Content-Type and Content-Range fields. The parts are separated using a MIME boundary parameter. It allows for binary as well as 7-bit and 8-bit files to be sent as multiple parts with the lengths of the parts being specified in the header of each part. Note that while HTTP makes provisions for using MIME for HTTP documents, HTTP is not strictly MIME-compliant.
Multipart/related can be used for compound documents where the object is built progressively from pieces, starting with the "root" body part as specified in the start parameter. If the start parameter is not specified, then the first body part is considered the starting point or "root" body part.
Multipart/related requires a type parameter. The type parameter specifies the content type of the first or "root" part.
Multipart/related processing takes precedence over content-disposition. Many MIME user agents do not recognize multipart/related and treat these messages as multipart/mixed. To allow for this, some UAs will include the technically unnecessary Content-Disposition header in multipart/related body parts.
Content-Location and Content-Base headers are defined to resolve URL references to other body parts. Both headers are valid in any message or body part. They are valid for the content heading or message heading where they occur and for its content.
The Content-Location and Content-Base headers apply to headers and body parts where they occur and do not have meaning in multipart headings.
The Content-Base header gives a base for relative URIs occurring in other heading fields and in HTML documents that do not have any BASE element in its HTML code. Its value must be an absolute URI.
The Content-Location header contains a URL that specifies the body of that body part. The URL may be relative to a URL specified in a Content-Base header.
The following example shows how these headers are used:
Content-Type: Multipart/related; boundary="boundary-content_example"; type=Text/HTML; start=example@somplace.com ;Content-Base header not allowed here ;since this is a multipart MIME object --boundary-content_example Part 1: Content-Type: Text/HTML; charset=US-ASCII Content-ID: <example@somplace.com> Content-Location: http://www.webpage/images/the.one ; This Content-Location must contain an absolute URL, since no base ; is valid here. --boundary-content_example Part 2: Content-Type: Text/HTML; charset=US-ASCII Content-ID: <example2@somplace.com> Content-Location: the.one ; The Content-Base below applies to ; this relative URL Content-Base: http://www.webpage/images/ --boundary-content_example--
The multipart/signed content type specifies how to support authentication and integrity services using digital signature. The control information is carried in the second of the two required body parts.
The multipart/encrypted content type specifies how to support confidentiality using encryption. The control information is carried in the first of the two required body parts.