A1 In the absence of any indication of the course to the next mark I asssume that by continuing close-hauled Red is sailing the course
Red's proper course is to sail close to the mark - she is given room to do so. 
Red is given room to pass the mark (nothing in the definition (b) requires a change of course.
Red is given room to leave the mark astern
Mark-room has been given

A2 When Red passes head to wind from port to starboard and is inside overlapped on Blue, Red becomes entitled to mark room under RRS18.2(c).
When Red luffs towards head to wind she breaks the overlap. RRS 18.2(c) ceases to apply. When Red passes head to wind Red and Blue are on opposite tacks on a beat to windward and therefore RRS 18 does not apply.
When Blue passes head to wind, RRS 18 applies. The boats are not overlapped, so RRS18.2(c) does not apply.  Blue, tacking then clear astern must keep clear. Red is subject to RRS 16, and, when she bears away she may become windward boat and required to keep clear of Red under RRS11

These are the real questions on the new rules i have myself. I will reflect and comment. No one has given answers and a call at a recent event highlighted this. I feel we may have been unsure of or decision as it was dependant on this new rule. Be in touch. 

Gordon, regarding my question Nr. 2: I agree with your analyses that in my scenario RRS 18.2(c) ceases to apply because the overlap is broken before Red passes head to wind. This means that my scenario does not provide a case where mark-room includes "room to tack". Can you think of another situation where mark-room results from 18.2(c) and includes room to rack? If not, can we indeed assume that deleting the last sentence of the definition does not change anything? 

PS: I am not yet totally convinced that Red, after passing head to wind, is still on a beat to windward, since she tacks around the windmark mark and bears away to sail the course to a leeward mark. 

Btw, in my post I tried out sailtalks.com, recently presented on this forum. Credits to Odey Hariri. 

Gordon, regarding my question Nr. 1: My concern was not whether mark-room was given to Red. My concern was whether Red was still sailing in her mark-room between passing the mark and leaving the zone, and whether she could exonerate herself against Blue luffing her under RRS 11. 

To Question 1, Red is required to tack to sail her proper course when match racing under App C 18.3(b). However, my opinion in a fleet race would be that Red has left the mark astern and Blue is then leeward boat and entitled to luff up to her proper course. Taking the opposite assumption to Gordon's first post, that this is a rounding mark, that proper course would include a tack. Tactically I, as Blue, might slow and tack behind Red, leaving me the leeward boat or clear ahead. But, as we say in France 'that depends' ... on so many other factors.

In Q1 Once Red has left the mark astern, mark room has been given so RRS18 ceases to apply under RRS18.1(b)
If the mark is a turning mark then the same argument applies - Red has been given room to sail close to the mark, she has been given room to round or pass the mark on the required side (but has chosen for some reason not to use that mark room). Red is now sailing outside the mark-room to which she is entitled so RRS 43.1(b) no longer applies). When Red leaves the mark-room astern, mark-room has been given and RRS18 ceases to apply.
In Q2. First, a warning about match racing rules and assumptions creeping into our rule interpretation. Match racing is a different game, with increasingly different rules and interpretations.

A boat is on a beat to windward while her course is close-hauled or above (see Case 132) Red is on a beat until she bears away below close-hauled. That includes the time when she was between head to wind and close-hauled. As Blue is also close-hauled they are both on a beat to windward until REd bears away.
I am always wary of referring to the original submission when trying to interpret a rule (see the magic disappearing hail in some intepretations of RRS20.2(b) which is the opposite to the interpretation in the submission). In this case the submission stated:
6. Removes the last sentence of the current definition (about room to tack). This resolves the debate among rules experts as to whether a boat is entitled to complete a tack after rule 18 ceases to apply; i.e., is she eligible or not for <exoneration= if she breaks rule 13 or 10 after passing head to wind.
Apparently, the new rule has not resolved the debate!

Gordon, on Q1: I find your analyses convincing, but still do not know how I can align it with the reasons given in the submission: "Makes it clear that if a boat leaves the mark astern before she has rounded or passed the mark as necessary to sail the course, she is still entitled to mark-room." Should we just ignore the reasons given for the change as erroneously?

On Q2: So what is our conclusion regarding the effect of deleting the last sentence? Would it make any difference if the sentence was still there? Are there any cases where a boat sails within mark-room while tacking? 

 Gordon, on Q1: I find your analyses convincing, but still do not know how I can align it with the reasons given in the submission: "Makes it clear that if a boat leaves the mark astern before she has rounded or passed the mark as necessary to sail the course, she is still entitled to mark-room." Should we just ignore the reasons given for the change as erroneously?

There are circumstances in which a boat must sail well beyond the mark before changing course to round it. For instance when sailing in 3 knots of current! The definition gives a boat the room to carry out such a manoeuvre

On Q2: So what is our conclusion regarding the effect of deleting the last sentence? Would it make any difference if the sentence was still there? Are there any cases where a boat sails within mark-room while tacking? 
The issue with the previous definition was that a boat was entitled to room to tack, but as soon as she passed head to wind she was no longer entitled to mark room (old rule 18.2 (d)). The call was that if there was an issue while the inside boat was tacking that meant that the outside boat was not giving mark-room before inside boat passed head to wind.
I think in most circumstances inside windward boat is entitled to luff to head to wind before losing entitlement to mark room ad will be exonerated for breaking RRS 11. Once she goes through head to wind she becomes keep clear boat, but the other boat is obliged to respect RRS 16 when changing course.

The Rules committee are trying to confuse us all from what we had previously believed.
I was with Gordon in that when you left the mark astern the mark room ceased.
However this is unsustainable and as you say does not follow 0130 23.
I think when the dust has settled the interpretation will be you do not leave the mark astern until you have rounded or passed it depending on the type of mark.
So in your post 1. mark room  is there till the boat leaves the zone..
If the boat does not round the mark however it is sailing outside the mark room to which it is entitled and no longer able to be exonerated as a windward boat.
It has no implicit room to tack. 
2. Mark room does not include room to tack. As it tacks (if the other boat does not tack, on a beat, it ceases to be overlapped and so !8.2C) does not apply. Once the other boat tacks,  there may be an overlap again then such rule may apply.

My reading is that a boat is entitled to:
- room to sail to the mark - if needed
- room to round or pass on the required side
-room to leave it astern
Once all 3 have been achieved mark-room has been given.
In exceptional circumstances a boat might have left the mark astern but not rounded it - for instance in a strong adverse current a boat may have to sail one or more boat lengths beyond the mark before turning to round it.

IN Q1 there is a vital item of information missing: the direction to the next mark. If Red leaves the mark astern while continuing on her course to the next mark (in this case without changing course) then mark room has been given when she has passed the mark and left it astern.