Boolean attributes are true whenever present, whatever their value. disabled="false" disables the control - the exact opposite of what the author intended, and one of the most persistent bugs in hand-written HTML.
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.