OCF Container

The Open Container Format (OCF) is the name of the ZIP file container that holds the resources of an EPUB publication (for both EPUB 2 and EPUB 3).

OCF, Container, EPUB Container and OCF Container are used interchangeably to talk about the ZIP file container for EPUBs.

Refer to the Open Container Format specification for more information.


OEBPS stands for Open EBook Publication Structure, the predecessor to EPUB 2.

Older applications still sometimes use the acronym OEBPS as the directory name where EPUB content is stored in the OCF container, but it is otherwise rare to encounter.

OPF file

OPF file is the abbreviated name sometimes used to refer to the EPUB 2 package document.

The acronym OPF comes from the name of the specification that defines the package document, the Open Packaging Format.

OPS Content Document

An OPS Content Document is the EPUB 2 version of the EPUB 3 Content Document.

Unlike EPUB 3, that allows both XHTML5 and SVG, OPS Content Documents are limited to XHTML 1.1

The acronym OPS comes from the name of the specification that defines EPUB 2 content documents, the Open Publication Structure.

Outline Algorithm

The HTML outline algorithm no longer exists.

It was conceived as a way of producing a consistent heading structure from an HTML document, but introduced navigation problems for assistive technologies.

The algorithm proved to be confusing for authors, however, and went unimplemented in user agents.