WPT details: Parsing test: https://github.com/web-platform-tests/wpt/blob/master/css/css-ui/animation/caret-animation-parsing.html It turns out that while caret blinking behavior does seem to be testable, doing so requires changing chrome to re-enable a blinking caret in web_tests, which was disabled many years ago due to the flakiness it caused. Given the cross-browser differences in blink rate testing seems unwise. Unit tests were used in the implementation.
Chromium supports animation of the caret-color property, but when animated the default blinking behavior of the caret interferes with the animation. For instance, see the example at https://drafts.csswg.org/css-ui/#caret-animation where an animation from blue to red and back is rendered as a blinking cursor that is randomly blue or red. The CSS caret-animation property has two possible values: auto and manual, where auto means browser default (blinking) and manual means the page author is controlling the caret animation. In addition, via a user stylesheet, it allows users who are disturbed by or have adverse reactions to blinking or flashing visuals to disable the blinking.
When the caret-color is animated the default blinking cursor interferes with the animation. This CSS property enables authors to disable the blinking when animating the caret color.
Explainers: https://drafts.csswg.org/css-ui/#caret-animation https://github.com/w3c/csswg-drafts/issues/9707