Etymological Note

The term Overlay itself, when applied to web technologies, has a history in W3C accessibility work, especially after 2009 (when WAI took on the task of helping develop accessibility support in HTML 5). The term may have seemed appropriate to name an approach that mirrored in web content the older practice where some hardware manufacturers provided (and still provide) transparent plastic sheets called braille overlays for touchpad controls, such as are typically found on microwave ovens. These braille overlays consist of transparent plastic with a sticky backside and appropriately located braille characters on their face. With the protective covering from the sticky backside removed, these braille overlays can be affixed onto the touchpad thus affording blind users reliable access to operating touchpad controls while not hampering visibility for sighted users. Similarly, the term was used in discussions of HTML 5 media and canvas accessibility. It is also sometimes used to describe the process of overlaying WAI-ARIA markup to add semantic information to existing content which otherwise lacks sufficient semantic clarity.

Overlays operate at the client side or presentation layer, effectively the “edge” of the web information flow, the final stage of the content collection and aggregation process that defines what is actually presented to end users.

As the Internet has grown, its users have come to expect speedy interaction and persistent connectivity—whether at home, or roaming in one's geographic locale, or even on international flights. The IT industry has happily promoted this expectation of persistent real-time access to data with actions such as removing memory card support from smart phones, among other initiatives encouraging dependence on cloud data storage. In turn this trend has made edge computing a core component of virtually every organization's IT strategy. While it is true that edge computing can enhance operational efficiency and automation, the need to maintain low latency for content load on user's devices heightens the demands for greater dependence on edge computing infrastructure. In this document we explore overlays as one approach to leveraging edge infrastructure for accessibility.

W3C Technologies on the Edge

How Overlays Function

Overlays are created with a JavaScript function within the code of a website. Any website author can add an overlay to their site, and third-party services strive to make it as simple as possible, such as this one from MailChimp.

An accessibility overlay that is intended to be visible to end users typically appears to the as a button in the corner of their browser window. The button remains in a static position as the user scrolls through the page. When it is activated, a user-interface appears with customization options that frequently include ways to change text size, text spacing and color contrast settings.

The extent of the user-side customizations available from an overlay will vary by vendor. Many accessibility overlays also perform automated functions whose complexity and actual benefit can vary widely,. It should not be surprising that poorly designed overlays can introduce more accessibility challenges for the end user than not having the overlay at all..

The Overlay Customer

It is also useful to acknowledge the customer-base for overlays. While even sizable corporations may have limited ability to employ accessibility expertise in their content development processes, frequently, the subscriber is a small business owner with a website created by an employee with no particular content development skills by using a fill out the form approach to content development—on a platform like WordPress, Wix, Shopify, or one of their many competitors. Small businesses choose these platforms because of their simplicity and low prices. Too often accessibility considerations aren'/ t front of mind for these businesses. Too often the platform providers do too little to help support accessibility; and, when they do support accessibility, obtaining an accessible outcome is too often a question of choosing the right set of templates.

Problems Solved By Overlays

Ensuring accessibility of websites and applications will ever remain a challenge. While everyone agrees that accessibility is best baked-in at the beginning of the digital content life-cycle, achieving accessible results will ever remain a work in progress simply because the ever more dynamic web will itself continue to be a work in progress.

With the proviso that we are assuming well crafted approaches, some useful applications of overlays include:

• Fixing legacy rendering. There are multiple reasons why a content provider may hesitate to apply fixes in source content—perhaps out of an abundance of caution to avoid unanticipated consequences from doing so.
• Support for an aging population. Many older citizens, often uncomfortable with technology in general, will not identify as persons with disabilities. Generally, they will not be users of assistive technologies. They may, however, be grateful for easily engaged colorization and contrast correctives, or a rerendering of content in more perceivable fonts. In the US, people aged 65 and older totaled 54.1 million in 2019 (or 16% of the population). By 2040, this age group is expected to grow to 21.6% of the population. This is a significant user base which should not be overlooked.
• Color and contrast, together with more perceivable font options, can be of benefit across all age groups. While there is a clear risk here of duplicating operating environment (or assistive technology) options, it may prove more fruitful to consider a complimentary approach rather than rendering judgement on which mechanism users should be required to know and use. One possibly invaluable future development between edge technology and system settings might be a privacy preserving secure mechanism to build user preference profiles that can be shared across all of a given user's devices. The both and opportunity here may well make the sum of the parts far more valuable than the traditional approach requiring independent settings on each individual device. we may do well to recall that Back buttons did not appear in web content because the user agents of that day lacked menu-driven mechanisms (or keyboard shortcuts) enabling the same feature.
• Website content authors may also benefit of accessibility overlays. Many website creators have little or noo development budget or digital accessibility experience, particularly small business owners. This group may sometimes rely on an accessibility overlay technology more than many accessibility professionals would prefer, but an overlay may be the only technology helping them in their specific situations.
• End users can be enabled by overlays to help fix challenges on particular pages, e.g. by proposing better alternative text, or otherwise commenting on barriers they've encountered on a particular page view.
• When the accessibility challenge is found to be linked to poor code in some open source library or application, a fix pushed and accepted to that code will likely remediate not only the challenge that triggered the report, but also all other sites using that library or helper application.

Overlay Antipatterns

EDITOR'S NOTE
This section needs more work.

It is to be noted that poorly designed overlays can actually work to impede accessibility. Some common antipatterns found in overlays include:

• the overlay might make frequent screen reader announcements regarding its functionality, announcements that would not be needed if there was no overlay present at all.
• Sometimes an overlay may activate certain features only when a screen reader is detected, causing the user to conclude that their disability, having been detected, will now also likely be recorded without their permission (a violation of basic privacy).
• A non-mouse or pointer user who routes on keyboard navigation may find the overlay received focus in unexpected ways, breaking focus order.
• Sometimes, most if not all of the CSS-modification features are available elsewhere on the host system (e.g. in the assistive technology, the browser (or other user agent), or in the host operating system itself). Offering capabilities redundantly on the page can tend to clutter up the page for no real reason while making their application a repetitive task as the user browses from one page to another, rather than a global configuration choice.
• Even overlay proponents who agree that CSS-alteration features (like dark mode) are desirable, providing value to people living with low vision, would tend to agree that the lack of standardization among various overlays may make this feature less usable because it's too often hard to locate.

Expanding the Approach

It has previously been noted that edge computing hasn's figured in the web content accessibility paradigm, though many remediation providers are increasingly testing with end users at the content delivery point rather than at the content server source. While testing with real users is clearly valuable, it can arguably be made even more valuable by supplementing with automated reporting. Meanwhile, identified problems may be remediable as noted above. Most important, however, is the careful consideration of how accessibility might leverage emerging industry application of W3CD authentication technologies to carry user content rendering settings across all user devices.

Though not all overlay solutions provider operate from the same paradigm, the following is offered as a high-level overview of content creation, updating, and delivery today along with some suggestions of additional ways overlays might function to benefit users.

1. A site is developed inconformance to WCAG Success Criteria and then launched for use.
2. Because today's web is dynamic, various content injections introduced before content is delivered to the end user may well to introduce accessibility challenges. Well crafted overlays (and perhaps other edge technologies) can help remediate many of the resulting challenges, and flag others for manual remediation.
3. Content is added to the site after completion from time to time, some of which may introduce accessibility violations. Well crafted overlays (and perhaps other edge technologies) can help remediate many of the resulting challenges, and flag others for manual remediation.
4. Meanwhile, the technologies used on the host site undergo further development, some of which may introduce accessibility challenges. A reporting overlay can be used to alert the site developers about them.
5. As time passes, new accessibility standards are introduced, resulting in some code on the site no longer being conformant. The reporting overlay may be used to remediate some non-conformant code, and alert site developers.

We emphasize that the use of overlays does not necessarily remove human expertise and oversight from a remediation process. But rather than perform the tedious and time-consuming task of identifying and remediating challenges by hand, humans can use overlays to make the traditional remediation process more efficient and comprehensive. This is already current practice for some overlay solutions providers today.