:is(). Following the specification pseudo elements are invalid and we now transform to a known invalid pseudo element.onPseudoElement plugin option. Set { onPseudoElement: 'warning' } to receive warnings when this plugin encounters an unprocessable pseudo element.@csstools/selector-specificity (major):before and other pseudo elements.@csstools/selector-specificity for specificity calculations.::before were moved.skip flag in onComplexSelectors option.If a complex selector is encountered that has no known equivalent, it will always be skipped and preserved now.
The previous behavior was to remove :is() even if that broke the selector.