https://www.cnbc.com/2018/07/12/how-an-obscure-british-regulation-called-the-chain-principle-is-chan.html

We're likely entering the end-game scenario for Comcast and Disney's pursuit of Fox's assets. However, an obscure U.K. takeover rule called the "chain principle" has altered the bidding dynamic in what's become a game of three-dimensional chess.

The U.K. has different rules around mergers and acquisitions than the U.S. One of these rules is a lesser-known guideline called the chain principle. The idea is that if a target company's ownership is split, and a would-be acquirer bids on one portion of the target, the implied value of the portion of the company that received the takeover offer must be carried over to fairly value the rest of the company.