Complex images and alt text descriptions

Complex images like charts & graphs must be briefly described using basic alt text and must have a more complete long description elsewhere in the page. The long description should be available to both sighted and screen-reader users and be programmatically associated with the image.

The figure / figcaption method:

One of the limitations of basic alt text is that it’s meant to be brief, no more than around 150 characters. So you shouldn’t try to use an alt attribute in an image for the long description. Instead, a good way to add a programmatically associated long description is the use the figure / figcaption method. In this method the figure tag wraps the whole image and long description code. Then the figcaption tag is used to wrap the long description text. This can be normal HTML text that’s available to both sighted and screen reader users. Inspect the code of this preformatted example to see how the figcaption tag is used house a long description.

Pie chart showing factors affecting credit scores. See table next to this image for the data.

Factors in Your Credit Score

Payment History (35%) 35%
Outstanding Debt (30%) 30%
Credit History (15%) 15%
Pursuit of New Credit (10%) 10%
Types of Credit in Use (10%) 10%

The aria-describedby method:

You can also use the aria-describedby attribute added to an image to point to the id of a long description. For example, you could point to the id of a div wrapping a long description like:

    Pie chart showing factors affecting credit scores. See table next to this image for the data.


Factors in Your Credit Score

Payment History (35%) 35%
Outstanding Debt (30%) 30%
Credit History (15%) 15%
Pursuit of New Credit (10%) 10%
Types of Credit in Use (10%) 10%

Inspect the code of this preformatted example to see how aria-describedby works. In this example, the table within the wrapper div describes the segments of the pie chart. It wouldn’t be possible to descibe all those segments in basic alt text.

The web accessibility guideline SC related complex images is 1.1.1 Non-text Content (Level A). The W3C WAI has a tutorial with more information about handling complex images. Most universities are striving to meet WCAG level AA conformance. Of the three levels of WCAG conformance, level A is the most important to achieve and level AAA is nice to have but not mandatory. So level AA is a middle ground that most universities and government agencies strive to achieve. Ohio State’s information about minimum web accessibility standards can be found in the Digital Accessibility Center’s website.

Comparing screen readers: VoiceOver and NVDA

VoiceOver for Mac and NVDA for Windows are two popular screen readers helping users with visual disabliites navigate websites. They share some similarities and have some differences. VoiceOver’s rotor and NVDA’s Insert+F7 function fullfill a similar purpose.

The basics:

To launch VoiceOver, click Command+F7. To a launch NVDA, click Control+Alt+N.

In VoiceOver you use VO + Right Arrow to read the next item while in NVDA you use the Down Arrow.
In VoiceOver you use VO + Left Arrow to read the previous item but not in NVDA.

The rotor:

The rotor in MacOS VoiceOver is similar to NVDA’s Insert+F7 function in that it allows the user view and to jump to headings, landmarks, or other HTML elements. To popup the rotor in MacOS VoiceOver presss VO + U. ‘VO’ is the VoiceOver keys (Control & Option) that are pressed in conjunction with a VoiceOver command (like U which launches the rotor). Use the Left and Right arrows to select page elements like: Links, Headings, Tables, Frames, Images, Form Controls, Landmarks, Visited Links, and Non-Visited Links. Once a page element type is selected, the Up and Down arrows can be used to select a particular element from the list and Enter can be used to activate it. The Escape key exits the rotor.

An example of the rotor in MacOS Voiceover poping up a list of headings.

An example of the rotor in MacOS Voiceover poping up a list of headings.


Configuring the rotor

You can choose which element types are viewable in the rotor by opening the VoiceOver Utility with VO + F8, then going to ‘Web’ > ‘Web Rotor’. VoiceOver for iOS devices also has a similar rotor that can be configured.



Features similar to the rotor in other screen readers:

Popping up a list of all links in other screen readers is similar to what the rotor does in MacOS VoiceOver. Insert+F7 in NVDA can pop up a list of all links.

To list all links in MS Narrator, hit Caps Lock + F7 or Insert + F7. See Deque System’s information about MS Narrator for info about keyboard shortcuts.

To list all links in JAWS for Windows, hit Insert + F7. See Deque System’s information about JAWS for info about keyboard shortcuts.

ARIA Menu or Menu bar interaction pattern recomendations

Many websites use Menu or Menu bars for their global navigation to pages in the site. For maximium accessbility it’s best for these menu bars to follow ARIA APG guidelines. In ARIA APG’s recommended menu interaction pattern, because menubar and menu elements are composite widgets as described in Keyboard Navigation Inside Components, Tab and Shift + Tab don’t move focus among the items in the menu. Instead arrow keys are used to move through the menu items and the Enter key is used to follow a link. The right arrow goes to the next item and the left arrow moves focus to previous item. See ARIA APG’s recommended menu interaction pattern for more details about how the arrow keys should behave. Using ARIA APG guidelines as a standard way of building menus will help establish a web convenion that users can learn and apply to a lot of website. Using a standard interaction pattern convension for menus will save users time in not having to learn a different interaction pattern.

ARIA menu and interation pattern resources

What’s new in WCAG 2.1?

The Web Content Accessibility Guidelines (WCAG) are a set of globally adopted technical standards on web accessibility developed by the World Wide Web Consortium (W3C). The guidelines represent a shared, international standard developed by many different stakeholders including: education, industry, disability organizations, government, and accessibility research organizations. The guidelines strive to make websites, apps, electronic documents, and other digital assets accessible to people with a broad range of disabilities, including sensory, intellectual, learning, and physical disabilities.

WCAG covers a breath of success criteria that, when followed by website designers, developers, and content authors, can remove many of the barriers that people with disabilities face when navigating a website or other digital applications. Find out more about WCAG in this article – WCAG 101: Understanding the Web Content Accessibility Guidelines.

What are the new accessibility guidelines in WCAG 2.1?

WCAG 2.1 became a W3C Recommendation in June 2018. There are 17 new SC (success criteria) guidelines in WCAG 2.1:

  1. 1.4 Reflow (AA) – responsive design principals are important to accessibility.
  2. 1.4.11 Non-text Contrast (AA) – requires the icons, UI, and graphics should have good color contrast.
  3. 1.4.12 Text Spacing (AA) – the Text Spacing bookmarklet can help test.
  4. 1.4.13 Content on Hover or Focus (AA) – don’t show unexpected content on hover.
  5. 2.1.4 Character Key Shortcuts (A) – don’t interfere with screen reader shortcuts.
  6. 2.5.1 Pointer Gestures (A) – complex gestures also need a single pointer equivalent.
  7. 2.5.2 Pointer Cancellation (A) – down events must not be used to complete a function.
  8. 2.5.3 Label in Name (A) – visible labels should match the accessible name.
  9. 2.5.4 Motion Actuation (A) – don’t make shaking the phone the only way to complete an action.
  10. 4.1.3 Status Message (AA) – alert the user, but don’t interrupt them.
  11. 1.3.6 Identify Purpose (AAA) – HTML content should provide context, purpose and meaning.
  12. 2.2.6 Timeouts (AAA) – you must store the user’s data for 20 hours.
  13. 2.3.3 Animation from interactions – motion animation trigged by interaction can be disabled. Use media query: prefers reduced motion.
  14. 2.5.5 Target Size (AAA) – touch target size must be 44 x 44px.
  15. 2.5.6 Concurrent Input Mechanisms (AAA) – websites should allow users to switch between input modalities.

Here’s a Good video covering all things new in WCAG 2.1 (53:58).

What are the main WCAG principals of accessibility?

The top four principals of WCAG are: perceivable, operable, understandable, and robust. All new guidelines introduced fall under one of these broad categories. WCAG 2.2 is scheduled to be completed in early 2023 and will include 12+ new guidelines.

  1. Perceivable – people must be able to find your content.
  2. Operable – people must be able to use your website.
  3. Understandable – people must be able to understand your website.
  4. Robust – your website must work with different assistive technology.

See Understanding the Four Principles of Accessibility for more info.