I would advise against concealing the objects present until you examine the room; the standard way for the player to look at what's in the room itself is through the "look" command, which simply prints the room description. If your room is called (say) The Library, very few players will think of typing "x library."
Making them examine things that are discussed in the room description is usually fair game, though. If your supporters are scenery (see section 3.8), then you can just remove the rule that makes the room description print the things that are on scenery supporters, thus:
Code:
The describe what's on scenery supporters in room descriptions rule is not listed in any rulebook.
If you have supporters that aren't scenery, then I think this should work:
Code:
Rule for printing the name of a supporter when listing nondescript items:
say "[printed name of the item described]";
omit contents in listing.
See sections 17.10 and 17.23 for more about what's happening there. Something similar should work for containers, I think.
You should be a little careful about this -- players have been known to get annoyed when the room description lists a table but not a plot-critical vase that's on the table, when the vase is in plain sight too.