Reflow

About

Version:	WCAG 2.1 and up
Number:	1.4.10
Level:	AA
Applicability:	Fixed Layouts
Requirement:	Content can be presented without loss of information or functionality, and without requiring scrolling in two dimensions for: Vertical scrolling content at a width equivalent to 320 CSS pixels; Horizontal scrolling content at a height equivalent to 256 CSS pixels. Except for parts of the content which require two-dimensional layout for usage or meaning.
Guidance:	Understanding Success Criterion 1.4.10 How to meet Success Criterion 1.4.10
Techniques:	C31: Using CSS Flexbox to reflow content C32: Using media queries and grid CSS to reflow columns C33: Allowing for Reflow with Long URLs and Strings of Text C38: Using CSS width, max-width and flexbox to fit labels and inputs G206: Providing options within the content to switch to a layout that does not require the user to scroll horizontally to read a line of text SCR34: Calculating size and position in a way that scales with text size

Purpose

The purpose of this success criterion is to ensure that readers with low vision can read a publication without having to scroll in two dimensions when zooming the content to 400%.

How to Meet

Authors need to ensure that as their publications are zoomed the content reflows to fit the available area (e.g., the content is not clipped by the edge of the page). Users should not have to scroll to read a line of text (e.g., scrolling from side-to-side to read text that is read horizontally, or top-to-bottom for text that read vertically).

For reflowable EPUBs, this usually only requires techniques that force content into a fixed area. Examples include using absolute units of measure such as pixels so that container elements cannot resize into the available space and using static layouts such as design tables that cannot adapt as the screen space shrinks.

Meeting this requirement for fixed layouts is much more complicated depending on the type of content. Image-based content, where the presentation is essential to the understanding (e.g., comics and manga) are exempt from the requirement, but all other fixed layouts are not. But as EPUB reading systems do not re-render pages as they are zoomed, only increase the magnification, nothing an author does will make these publications accessible (i.e., scrolling is unavoidable).

Note that this success criterion only applies to desktop computers with a screen resolution of 1082px by 1024px. It is not required that the content be zoomable to 400% on mobile devices of any screen resolution.

Additional Information

The following knowledge base pages provide more information about how to address this success criterion for publishing content:

Reflow