Fixed-layout publications can be created using HTML documents to combine text and images. Each document is assigned a fixed height and width, the canvas on which the content is positioned. CSS is used to absolutely position content elements within this display area, or images are embedded in the page that fit the dimensions.
The advantage of using HTML for fixed layouts is that it makes the text content of each page available to assistive technologies. In the case of images, it allows the native accessibility techniques HTML affords to be used to provide alternative text and extended descriptions.
Although it is possible to create fixed layouts on the Web, they are not naturally supported by browsers. A browser will render the page as designed but not make any optimizations to support the rendering.
To fix this problem for publishing, EPUB 3 introduced metadata to aid reading systems in creating the appropriate display area and characteristics for each fixed layout page.
EPUB publications can consist entirely of fixed layout XHTML pages or there may only be a few fixed layout pages interspersed in a reflowable publication (e.g., a map might be included as a fixed layout in an otherwise reflowable publication).
It is also possible to mix fixed-layout SVG pages with fixed-layout XHTML pages, or with images directly in the EPUB reading order.
Refer to the fixed layouts overview page for more information about how fixed-layout publications are created.
The same practices that make reflowable publications accessible are used to create fixed layout HTML pages with the greatest accessibility. Some key practices include:
- Ensuring the logical reading order — The order of content must match the order that the user would logically be expected to encounter it on the page. Use CSS to arrange the position on screen.
- Avoid splitting content across pages — although there are some methods to make page spreads accessible, when supplementary information, like sidebars, are split across pages it makes retaining a logical reading order difficult.
- Using structural markup — Makes sure the content is marked up meaningfully so it can be navigated by assistive technologies. For example, use heading and table markup instead of styling content to look like these structures.
- Describing all meaningful images — All images that contain information necessary to understand the publication must be described using alternative text and/or extended descriptions. Background images often provide context for character interactions, so dialogue may not make sense without the scene setting.
- Avoiding images of text — Layering text over top of a background image makes it accessible to assistive technologies.
- Ensuring text contrast — Because fixed layouts often involve the layering of text over images, it is important to ensure that the text is visually distinguishable from its background.
Even when following these practices, a key problem that limits the accessibility of fixed layouts is that reading systems often lock out users from changing the appearance of the documents to preserve the author's layout (e.g., disabling the ability to increase font size or changing text color). As a result, even the best efforts to make a fixed-layout publication accessible may still leave it unreadable to some users.