climbing

climb (climbing) handles climb X, climb up/down X, scale, ascend, descend X, all gated on the climbable trait (climb into the basket is entering; climb out is exiting). Climbing something puts you on it, the same place putting yourself on an enterable supporter gets you; an unclimbable target refuses with not_climbable, and trying to climb something you are already on refuses with already_there.

The author writes:

create the Orchard Corner
  a room

  One great pear tree leans over the garden wall here.

create the pear tree
  aka tree
  a supporter, climbable
  scenery
  in the Orchard Corner

  Low branches all the way up, practically a ladder.

  after climbing it
    phrase over-the-wall
      From up here you can see clear over the wall into the lane.
  end after

create the garden wall
  aka wall
  scenery
  in the Orchard Corner

  Twelve feet of smooth brick, no handholds.

create the player
  starts in the Orchard Corner

The player sees:

> climb the wall
You can't climb the garden wall.

> climb the tree
You climb onto the pear tree.

From up here you can see clear over the wall into the lane.

> climb the tree
You're already on the pear tree.

> climb out
You get out of the pear tree.

The supporter composed alongside climbable is what makes the perch real, somewhere to actually be, so the second climb can refuse and climb out has something to leave; with bare climbable alone the climb speaks success but the player never leaves the room floor (nothing can hold them).

Interceptors: after climbing it on the target, the pear tree's comment above, and how a cliff would teleport (below). There are two honest footnotes. First, the action also implements directional climbing (climb up meaning "take the up exit"), but no core grammar reaches it today: bare up/down parse as going, which is usually what you want, and a story adding climb up as grammar gets room-exit climbing for free. Second, the trait's destination/direction fields are unread by the standard action, so climbing never teleports you to a destination room; put an after climbing it clause on the cliff if you want that (blockedMessage/successMessage are likewise story data).