A container is the single file used to bundle the resources of a digital publication together.

As digital publications are made up of many different files — HTML documents, images, CSS files and scripts, among others — bundling them together into a single container makes it simpler to distribute publications (e.g., only one file has to be sent to a vendor or downloaded by a user to get the entire publication).

EPUB, for example, uses ZIP as its container format.

Content Provider

The organization responsible for providing a digital publication to users, whether through an sale in online bookstore, by download from a corporate web site, through a library lending program, or otherwise.

Core Media Type

In EPUB 3, a core media type is a file format that reading systems are required to support when used in EPUB content documents. Using core media types helps ensure that publications will be readable in whatever reading system a user happens to use.

For example, EPUB 3 requires reading systems that support audio playback be able to render MP3 and MP4 audio. Similarly, reading systems with viewports are required to support a variety of image formats. These are all core media types.

If the media type of a resource is not listed as core, it is considered a foreign resource (i.e., reading systems might support it, but are not guaranteed to).

The list of core media types supported in EPUB 3 is provided in the EPUB 3 specification.


The Cascading Style Sheet (CSS) language is used to control the visual presentation of HTML and SVG documents.

CSS is used to specify fonts, colors, borders and other display aspects based on a set of rules defined by the author.