The footnote was easy to miss. It began on page 27 of Exxon Shipping Co. v. Baker, issued by the Supreme Court on June 25, and it ended on the next page.

But Justice David Souter’s footnote 17 has reverberated around law schools, leading Hugh Young, a lawyer involved in the landmark punitive damages case, to predict that “it is going to become the great mystery footnote of the decade.”