A new definition called Mark-Room.

Instead of saying “room at the mark,” there is a new concept called “mark-room” (see definition Mark-Room). In fact, it is not entirely new; the previous rule 18 contained a definition of room at a mark or obstruction that has now been incorporated into the new definition. “Mark-room” is the space a boat needs to sail “to” the mark in a seamanlike way; and then when she’s “at” the mark, the space she needs to sail her proper course around the mark. The primary difference is that the previous rules did not specifically require outside right-of-way boats to give inside boats room to sail “to” the mark, though most outside boats did so anyway. Once a boat gets to the point where she needs to turn around the mark, she can sail her fastest course from that point on (i.e., her proper course), which will normally be to smoothly turn around the mark passing as close as she dare. There is not much game change here.