For example, here is a snippet from the game I am playing on that site (Hootuk is my character and he is being introduced in this post):
By the way, I used the 'imgurl' tag to display the map... sweet!'Here's where you went last time in:
Hootuk, feel free to introduce yourself now.
[Private to Hootuk Thadyyz: Only you and I can see this private line. You can send one using the bar at the bottom right-hand corner of the box you type in. "Insert a private line to:" You can send to another player (like if the two thieves scout together out of earshot of the others) or to me if you're doing something you don't want the others to know about. It's a cool feature of this site - one of many. ]'
Anyway, as for the above, the DM composed his post and included, within the same post, a private message directly to me. It's a pretty cool feature and one that would be pretty useful. A DM could prompt a particular character to make a an ability check (or saving throw, or surprise roll, or ask them to check for a trap, etc...) directly in the same post, without needing to compose a separate PM to that player (which also helps preserve context).
Low priority, if even possible, but you did ask for suggestions.
