All functionality must be operable through a keyboard interface. This is a static structural indicator for success criterion 2.1.1; the live WCAG engine performs the full runtime evaluation when a browser is available.
Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.