Based on a conversation between Alice Boxhall, Brian Kardell and Marcy Sutton, this prototype attaches/manages metadata in the form of a modality attribute to the body, as a way to allow authors to experiment with adapting style based on the user's active input modality (i.e., how they are interacting with the UI right now).
Rationale
There are many instances in which it would be useful for authors to understand the user's current interaction modality and be able to adapt the UI with better accomodations. The motivating example is :focus where the status quo is quite problematic:
- The default focus ring is not based on a single :focus rule as some might expect, not all things which can receive focus receive a ring in all cases. Adding such a rule is always currently problematic, but it's also exceptionally common.
- Many developers disable the default focus ring in their CSS styles, others attempt to style it in concert with their design. The former often seems to be a result of finding the default focus ring both aesthetically unpleasant and confusing to users when applied after a mouse or touch event and introduces accessibility problems. The latter inevitably creates considerably more of the kind of problem that the former was trying to solve.
To deal with this:
- It seems evident that a visual indication of what has focus is only interesting to a user who is using the keyboard to interact with the page. A user using any kind of pointing device would only be interested in what is in focus if they were just about to use the keyboard - otherwise, it is irrelevant and potentially confusing.
- Thus, if we only show the focus ring when relevant, we can avoid user confusion and avoid creating incentives for developers to disable it.
- A mechanism for exposing focus ring styles only when the keyboard is the user's current input modality gives us this opportunity.
Implementation Prototype
At this stage, we're only looking at keyboard modality.
The tiny keyboard-modality.js provides a prototype intended to achieve the goals we are proposing with technology that exists today in order for developers to be able to try it out, understand it and provide feedback. Simply speaking, it sets a modality=keyboard attribute on body if the script determines that the keyboard is being used. Similarly, the attribute is removed if the script determines that the user is no longer using the keyboard. This allows authors to write rules which consider the input modality and style appropriately.
It also simulates how the default UA styles would be adjusted by appending the following style as the first rule in the page, which disables the focus ring unless modality is set to keyboard:
body:not([modality=keyboard]) :focus { outline: none;}(This is added in a <style> element with the ID "disable-focus-ring", to allow easy removal if different behaviour is desired.)
How it works
The script uses two heuristics to determine whether the keyboard is being used:
- a
focusevent immediately following akeydownevent - focus moves into an element which requires keyboard interaction, such as a text field
- TODO: ideally, we also trigger keyboard modality following a keyboard event which activates an element or causes a mutation; this still needs to be implemented.
Custom elements may use the supports-modality attribute to provide a whitelist of supported modalities; any element without this whitelist is considered to support all modalities. Only elements which only support keyboard modality will trigger the modality=keyboard attribute on <body>.