Identifying the Part Content Type

The package implementer shall define a format mapping with a mechanism for associating content types with parts. [M2.3]

Some physical package formats have a native mechanism for representing content types.

example: : the content type header in MIME For such packages, the package implementer should use the native mechanism to map the content type for a part. [S2.1]

For all other physical package formats, the package implementer should include a specially-named XML stream in the package called the Content Types stream. [S2.2] The Content Types stream shall not be mapped to a part by the package implementer. [M2.1] This stream is therefore not URI-addressable. However, it can be interleaved in the physical package using the same mechanisms used for interleaving parts.