Parts in an Open Packaging Conventions Package may contain any type of data. This may include text, images, binaries, XML and other data. Parts are analogous to a folder in a file system. The organization of this “filing system“is left to the user and may be whatever is convenient for the application.

The name of a Part must be unique and URI-addressable. The content of the Part is described using a MIME-style media type. The media types of the Part referred to as the Content_Types in the ISO/IEC 29500-2:2021 specification are stored in the Package in an XML file named “/[Content_Types].xml”.

The content stored in a Part is identified by the Content-Type. Every Part of a Package has a Content-Type.