Single flash
Core requirement
Content does not include a change of contrast (over 4.5:1) going from light to dark (or dark to light) of more than 30% of the visible content area (viewport).
Except when
This is a new provision for a big, intense, single on/off flash. This is reported as a trigger by group members, but we need data on this, and a definition that includes size/intensity to avoid including non-triggers such as menus.
This provision relies on the color contrast algorithm in WCAG 2. When the algorithm is updated for WCAG 3, the contrast metric will also be updated.
Intent
To be added
Methods
- Design content without large changes of contrast. For example, when a menu with a light background is opened, it opens over a light background. Videos do not go from a dark to light background in less than a second.
Procedure
For each change of contrast:
- Check if the change of contrast is triggered by a loading a new page/view.
- Check that the change of contrast is less than 4.5:1.
- Check that the area of the change of contrast is less than 30% of the viewport.
Expected results
#1, #2, or #3 is true.
Key Terms
- actively available
available for the user to perceive and use
On the web, “actively available” is content that is not inert (see explanation of inert in HTML).
- component
grouping of elements for a distinct function
- conformance scope
A product, set of Pages/Views, content, functionality, or components selected to be part of a conformance claim. Where a View or Page is part of a Process, all the Views or Pages in the process must be included.
How a person or organization selects the set is not defined in WCAG3. There maybe informative guidance on selecting a suitable set in future (similar to WCAG-EM), but regional laws or regulations may provide a methodology.
- content
information, sensory experience and interactions conveyed
- essential to outcome
always necessary to achieve the same result
If something is essential to the outcome then: If it were removed, the information or functionality of the content would be fundamentally changed, and the information and functionality cannot be achieved in another way that would conform
- page
non-embedded resource obtained from a single URI using HTTP plus any other resources that are used in the rendering or intended to be rendered together
Where a URI is available and represents a unique set of content, that would be the preferred conformance unit.
- platform
software, or collection of layers of software, that lies below the subject software and provides services to the subject software and that allows the subject software to be isolated from the hardware, drivers, and other software below
Platform software both makes it easier for subject software to run on different hardware, and provides the subject software with many services (for example, functions, utilities, libraries) that make the subject software easier to write, keep updated, and work more uniformly with other subject software.
A particular software component might play the role of a platform in some situations and a client in others. For example a browser is a platform for the content of the page but it also relies on the operating system below it.
The platform is the context in which the conformance scope exists.
- process
series of views or pages associated with user actions, where actions required to complete an activity are performed, often in a certain order, regardless of the technologies used or whether it spans different sites or domains
- view
content that is actively available in a viewport including that which can be scrolled, zoomed, or panned to, and any additional content that is conditionally shown while leaving the rest of the content in the viewport actively available
- viewport
object in which the platform presents content
The author has no control of the viewport and almost always has no idea what is presented in a viewport (for example, what is on screen) because it is provided by the platform. On browsers the hardware platform is isolated from the content.
Content can be presented through one or more viewports. Viewports include windows, frames, loudspeakers, and virtual magnifying glasses. A viewport may contain another viewport. For example, nested frames. Interface components created by the user agent such as prompts, menus, and alerts are not viewports.