OK .. I'll have a whack at it :-) (emphasis in rules added)

A1: a mark
A2: Because ....

  

A3: "left to Port" or "left to Starboard" (the "left to" puts the port and starboard relative to the boat).  
The language in Appx S7.2 is suggested as follows .. 

A4: Not if the meaning is applied in the context of def:sail the course, which requires the application/analysis of the taut-string of the boat's track after navigating the course.

The image from the other thread.  The mark below is "left to port" by the Yellow boat.

PS: And of course Happy Holidays to all my friends on RRoS.org .. wherever you are or whatever you do to celebrate this season!!! - Ang

My best guestimate .... have another drink.... it's almost Xmas ..... do not steer & sail while you are drunk ..... that will lead to a DSQ rightaway ! after the alcohol drug test after the race ......

1) the mark
2) mark is the nearest noun in the sentence. It would require a different construction to refer to the boat or anything else's side. 
3) it's conventional to say left to port if the mark is being rounded anti clockwise and vv. 
4) if I knew it wouldn't be unexpected [grin] 

Thanks for the replies guys & to Gjis for the seasonal alternative !
Q1. Two of you have said "the mark" and you may be right. It would be a lot clearer if the sub def made it crystal clear. Incidentally, as Angelo noted, the Def Sail the Course last line implies that it should be the required side of the boat.
Q2. Interesting answer Angelo. You have used J2.1 & Appx S7.2 to avoid having to avoid having to state the required side as required by the sub Def. However you also quote the Def Sail the Course which in (b)(1) complicates it again by stating "passing the mark on the required side", which again begs the question "required side of what ?". On Q2 Jim has stated what we normally do but has not stated what the required side is, as required by the Mark Room sub def (b).

If you are both right & the answer to "of what?" is the mark, then for a boat to "leave" it to port, it has to be stated that the required side is starboard, so that the boat passes the mark on the mark's starboard side (the boat's port side). Can you imagine the chaos if we state in the SI that the required side of the WM is starboard, when we expect the mark to be left to port ? Yet that is what the sub Def requires if the noun involved is the mark !

To make sense of the contradictions between the new Def Mark Room (b) & the Appx J & S provisions, sub Def (b) should be amended to : "to round or pass the mark on the required side of the boat, and". This would then make it crystal clear and the Def * the Appx J & S provisions would all work as we expect them to. Meanwhile, the solution as you have implied is not to state what the required side is at all, but to fudge it by using the words "to be left to port" etc instead !!

I suppose I haven't grasped something, but I don't see what the issue is. Maybe it's because personally I find the grammar sufficiently clear that I'm having trouble visualising it as 'the required side of the boat', but either way, as Angelo says, the SIs are mandated to tell us which way to sail the course. So, in my head, the path of room to be given is exactly the same whether I plumb in 'required side of the mark' or 'required side of the boat' into the definition. 

Robin we have "leave to port",  "leave to starboard", and now "leave astern".  Your discussion brings me back to the premise of my previous thread about "to leave astern". 

I think it confuses things that def:MR uses "to leave" when talking about "astern", simply because the other instances we use "to leave" is in a sail-the-course based thought process, and applying "to leave astern" in a sail-the-course way seems either nonsensical or at the least, trivial. 

To me it would have been more consistent with the rules and Cases to have MR culminate with "room to clear the mark", since that is the wording in def:racing.