Adding a new kind of supporter called a perch, where everything dropped lands on the floor.

Inform's default assumption is that if a player on an enterable object drops something, the dropped article winds up beside him on the same supporter or in the same container. This makes lots of sense for a dais, say, or a king-sized bed. It's a little less sensible if the enterable supporter in question is a bar stool or the like. So suppose we want to add a new kind of supporter called a perch, where everything dropped lands on the floor.

There are actually several ways of implementing this, but one of them is to reach right into the drop action and replace the "standard dropping rule" with a different one of our own invention – like this:

"Swigmore U."
Moe's Tavern is a room. The bar is an enterable supporter in Moe's. A drink is a kind of thing. On the bar is a drink called a flaming Homer.
A perch is a kind of supporter. A perch is always enterable. The stool is a perch in Moe's.
The player carries a dead field mouse and a tomacco fruit.
The sophisticated dropping rule is listed instead of the standard dropping rule in the carry out dropping rulebook.
This is the sophisticated dropping rule:
   if the player is on a perch (called the awkward position):
      let place be the holder of the awkward position;
      move the noun to the place;
   otherwise:
      move the noun to the holder of the player.
Test me with "sit on stool / drop mouse / look / get up / look".
Test me with "sit on stool / drop mouse / look / get up / look".
Moe's Tavern
You can see a bar (on which is a flaming Homer) and a stool here.

>(Testing.)

>[1] sit on stool
You get onto the stool.

>[2] drop mouse
Dropped.

>[3] look
Moe's Tavern (on the stool)
You can see a dead field mouse and a bar (on which is a flaming Homer) here.

>[4] get up
You get off the stool.

Moe's Tavern
You can see a dead field mouse, a bar (on which is a flaming Homer) and a stool here.

>[5] look
Moe's Tavern
You can see a dead field mouse, a bar (on which is a flaming Homer) and a stool here.

Now the carry-out behavior of the dropping action has been changed, but we haven't had to interfere in the checks or reporting at all. The rest of the action works just as it always did.

Of course, maybe we do want to change the way the action is reported, to make it clearer to the player where the dropped article wound up:

The sophisticated report dropping rule is listed instead of the standard report dropping rule in the report dropping rulebook.
This is the sophisticated report dropping rule:
   say "You drop [the noun] on [if the holder of the noun is a room]the ground[otherwise][the holder of the noun][end if]."