Look at the law to explain that a kick where the ball hits the post and the ball lands in the playing area, the ball is still in play.
With that (hopefully meaningful) assumption, the fact the grounding against the post is added in the law starts to make sense...
And the interpretation seen above: if grounded against the post, where is it grounded? make sense too.
Look at this in relation to the goalpost
If a loose ball touches a goal post on the field of play side of the post, the ball is not in goal
If a loose ball touches a flag post on the playing area side of the post, the ball is not in touch
If a ball being held by a player touches part way up the field of play side of a goal post, the ball is not in-goal
If a ball being held by a player touches part way up the playing area side of a flag post, the ball is not in touch
However
If a ball being held by a player touches part way up a goal post and then is slid down, and grounded on the field of play side of the base of the goal post, while still in contact with it, then the ball has been grounded in-goal.
so it stands to reason that,
If a ball being held by a player touches part way up a flag post and then is slid down, and grounded on the playing area side of the base of the flag post, while still in contact with it, then the ball has been grounded in touch.
This last sentence is what actually happened, and fits exactly what the law says for the ball to be in touch when grounded against the base of the post.
NOTE: I still maintain that if the Law makers had followed through with their original plan to place the flag posts on the
outside junction of the goal-line and touch-in-goal line (i.e. so that the flag post is completely outside the field of play with the inside of the padding in contact with the outside of the touch line) like it was during the 2008 ELV trials....
...then we would not be having this problem. A ball grounded against the flag post would have to be also touching the touchline and the decision would be easy.
Here is another interesting one.....
The padding is narrower than the width of the touchline, and a little of the line is "exposed". Would Kuridrani's try have still bee awarded if the flag posts were like this.