In this case, we’ll assume that Warped Foils is entitled to mark-room because he was overlapped with Masked Muffin when the action was frozen at the moment the first boat entered the zone. Being overlapped inside and to windward of a boat (MM) required to give him mark-room, WF’s mark-room includes room to tack.

This section of the Racing Rules of Sailing (RRS) used to have two rules: 18 Rounding and Passing Marks and Obstructions, and 19 Room to Tack at an Obstruction. Because the situation at marks tends to be very different from that at non-mark obstructions, rule 18 has been split into 18 Mark Room and 19 Room to Pass an Obstruction. Therefore Room to Tack at an Obstruction has now become Rule 20, (and Section D rules have been re-numbered 21 – 23.) A new preamble to Section C now informs us when rules 18-20 do not apply – most notably at our old friend, the starting mark surrounded by navigable water. Nothing has changed here. Allowing mark-room at starts would cause total chaos!

The new Rule 18 is re-worded and re-structured but it is basically unchanged in intent:
18.1 When Rule 18 Applies.
Rule 18 no longer begins apply when a boat is about to round which was not later than when the first boat entered the (two-length) zone but could also be earlier depending on boats and conditions. This was a judgment call for both sailors and protest committees that it was deemed desirable to eliminate. The new Rule is quite exact: Rule 18 begins to apply between boats at the moment “at least one of them is in the zone.” When does 18 not apply? As before, it does not apply “between boats on opposite tacks on a beat” or “between a boat approaching a mark and one leaving it”, not to mention your average start mark  - nor in a couple of other situations too esoteric to waste time on here.
18.2 Giving Mark-Room.
(a) the outside boat must give mark-room to an inside overlapped boat
(b) entitlement to mark-room 'locked in' when first boat reaches the zone > inside overlapped or clear ahead  at that moment is entitled to mark-room
(c) extent of a boat’s obligation to give mark-room: entitlement to mark-room 'locked in' for the duration of the rounding - unless either boat passes head to wind or if the boat entitled to mark-room leaves the zone
(d) if there is reasonable doubt, a claimed  last-second change in overlap status is to be denied [same as old 18.2(e)]
(e) if - from the time the inside overlap (established from clear astern) began - the outside boat has been unable to give mark-room, she is not required to give it

Except for the increased size of the zone, 18.3 remains unchanged in substance. Coming in along or very near the lay line, and then tacking to round continues to be actively discouraged by the rules makers: a boat that completes a tack to round the mark inside the zone has very few rights vis-à-vis a boat already fetching the mark on that tack. Specifically,
“The boat that tacked changed tack
(a) shall not cause the other boat to sail above close-hauled to avoid her or prevent the other boat from passing the mark on the required side, and
(b) shall give mark-room if the other boat becomes overlapped inside her”
18.4 Gybing.
As before, the inside boat must sail proper course at a gybe mark, i.e. gybe without undue delay. New rule not applicable at a gate mark. (Cannot figure out why this was necessary. click here for Gordon Davies' fine explanation of the gate mark exception in the UKWA Forum)
18.5 Exoneration.
If a boat that is taking mark-room to which she is entitled breaks rule 10 (port/starboard), 11 (windward/leeward), 12 (overtaking boat), 15 (giving initial room to freshly burdened boat), or 16 (course change by right-of-way boat), she shall be exonerated.

Bad news??? The obstruction definition now specifies that a “vessel under way, including a boat racing, is never a continuing obstruction.” This is the only rules change that makes me nervous, and here is why: Under the old rules, the passing-an-obstruction situation applied to a late-comer shoving his nose in from clear astern when the rest of us were already sitting side by side by side in the front row getting set to start. The late-comer used to only be allowed in if at the moment he established his overlap there was room for him to pass in safety between the windward boat and the leeward boat (which used to be a continuing obstruction vis-à-vis Windward). But under the new rules, the late-comer is only limited by Rule 15 (giving initial room to freshly burdened boat). A number of experts have expressed the fear that the boats in “Windward’s” situation will only be able to keep clear by moving forward and being over the line early. I have given this considerable thought and do believe that we can foil the accursed late-comer by line-sitting close together while pointing above close-hauled. That way, Leeward’s proximity would preclude Windward’s being able to bear away enough to get out of the way by moving forward across the line. Take that, late-comer!!! Al's late note: In the UKWA Forum, Gordon Davies points out that rule 19.2(b) should protect the windward boat here insofar as Windward will have been unable to give room from the time the overlap began: "(b) When boats are overlapped, the outside boat shall give the inside boat room between her and the obstruction, unless she has been unable to do so from the time the overlap began."
Apart from this, the rules for room at an obstruction remain unchanged:
 
19.1 When Rule 19 Applies: at an obstruction that is not a mark unless that mark is also a continuing obstruction in which case Rule 19 does apply.
19.2 Giving Room at an Obstruction
(a) right-of-way boat may choose to pass an obstruction on either side.
(b) outside boat must give room to inside overlapped boat; no zone involved; see also 18.2(e) re: inability to give room
(c) passing continuing obstruction – pretty much unchanged in principle
 
Rule 20
The procedure for giving/asking for “Room to Tack at an Obstruction” remains essentially unchanged. The basic routine is:  

Both penalty turns (fouls = 2 turns, touching mark = 1 turn) are now together in rule 44 while “penalty limits” which used to be in rule 44.4 are now more logically in 64.1 Penalties and Exoneration.
 
Gone from the RRS is rule 17.2 which prevented a reaching or running windward boat from sailing down to keep a leeward boat within two boatlengths of her from passing to leeward. I think this was a useful rule but word is that the rules makers felt that the rule was mostly ignored by competitors and thus perhaps no longer needed.
 
Note: The complete current text of the RRS is always available at and can be downloaded from the ISAF site at http://www.sailing.org/tools/documents/RRS2009-2012-[5950].pdf