Reading order: CSS positioning

Definition Elements positioned using CSS absolute, relative or fixed must maintain a meaningful reading order of content.
Purpose
  • If the reading order of text content on the page is presented to users of assistive technologies in an order that does not match the intension of the author, reading comprehension will be affected. In worst-case scenarios, the meaning of the out-of-order content may contradict or bear little resemblance to the intended meaning.
  • Assistive technologies render web page content based upon the sequence of the DOM elements within the HTML document.
  • Web page designs that rely upon table markup for layout or advanced CSS positioning techniques and JavaScript to rearrange content may result in a visual rendering of content that differs in reading order from the actual DOM ordering used by assistive technologies. Thus while the visual rendering may appear to have the correct or desired reading order, when rendered by assistive technologies such as screen readers, the actual reading order will be incorrect and correspondingly illogical.
  • The relationship of the DOM order of content to the intended reading order is therefore very important for ensuring that information is logically presented to users of assistive technologies.
Required Yes for HTML4 Legacy Techniques ruleset mapping
WCAG 2.0 Success Criteria

1.3.2 Meaningful Sequence (Level A, Primary Success Criterion)

Rule Category Styling/Content
Scope Page
Target Resources article, aside, div, footer, header, main, nav, section, table[role="presentation"]
Techniques
  • Minimize the use of CSS position values of absolute, relative and fixed.
  • Make sure related content moves as a block when repositioning content on a page.
Manual Checks
  • Disable layout tables (e.g. table[role="presentation"]) and CSS to make sure the content rendered has a meaningful sequence.
Informational Links