This specification, EPUB Open Container Format (OCF) 3.0, defines a file format and processing model for encapsulating the sets of related resources that comprise one or more EPUB® Publications into a single-file container.

This specification is one of a family of related specifications that compose EPUB 3, the third major revision of an interchange and delivery format for digital publications based on XML and Web Standards. It is meant to be read and understood in concert with the other specifications that make up EPUB 3:

• The EPUB 3 Overview [EPUB3Overview], which provides an informative overview of EPUB and a
• roadmap to the rest of the EPUB 3 documents. The Overview should be read first.
• EPUB Publications 3.0 [Publications30], which defines publication-level semantics and
• overarching conformance requirements for EPUB Publications.
• EPUB Content Documents 3.0 [ContentDocs30], which defines profiles of XHTML, SVG and CSS
• for use in the context of EPUB Publications.
• EPUB Media Overlays 3.0 [MediaOverlays30], which defines a format and a processing model for
• synchronization of text and audio.

OCF is the required container technology for EPUB Publications. OCF may play a role in the following workflows:

• During the preparation steps in producing an electronic Publication, OCF may be used as the
• container format when exchanging in-progress Publications between different individuals and/or
• different organizations.
• When providing an electronic Publication from publisher or conversion house to the distribution or
• sales channel, OCF is the recommended container format to be used as the transport format.
• When delivering the final Publication to an EPUB Reading System or User, OCF is the required
• format for the container that holds all of the assets that make up the Publication.

The OCF specification defines the rules for structuring the file collection in the abstract: the "abstract container". It also defines the rules for the representation of this abstract container within a ZIP archive: the "physical container". The rules for ZIP physical containers build upon the ZIP technologies used by [ODF]. OCF also defines a standard method for obfuscating embedded fonts for those EPUB Publications that require this functionality.

This specification supersedes Open Container Format (OCF) 2.0.1 [OCF2]. Refer to [EPUB3Changes] for information on differences between this specification and its predecessor.