MAC address in its two written conventions: six hex octets separated by colons or hyphens, and the Cisco dotted form of three groups of four. The separator is not back-referenced, so a string that mixes colons and hyphens also matches, which Presidio forbids with a backreference. Six hex pairs is a distinctive enough shape that noise stays low in prose, though a colon-delimited hex digest matches too. No collision with any existing pattern.