* Changing reachability
(Backdrops which can only be examined; Waterworld)
A backdrop which the player can examine, but cannot interact with in any other way.

It's tempting to handle the player's inability to interact with something with a simple instead rule:

	{*}"Waterworld 1"

	A view is a kind of backdrop. Instead of doing something other than examining to a view, say "You are too far from [the noun] to do anything but look."

	The sun is a view. It is everywhere. The description is "A blazing sun makes you wish you had never been born."

	The Sahara is a room. North of the Sahara is More Sahara. North of More Sahara is Yet Further Sahara.
	
	Test me with "x sun / get sun / n / x sun / n / x sun".

Unfortunately, the rule does not address the case where the object in question is the second noun; so for instance the following example reveals the difficulty:
	
	{*}"Waterworld 2"

	A view is a kind of backdrop. Instead of doing something other than examining to a view, say "You are too far from [the noun] to do anything but look."

	The player carries a rope.

	The sun is a view. It is everywhere. The description is "A blazing sun makes you wish you had never been born."

	The Sahara is a room. North of the Sahara is More Sahara. North of More Sahara is Yet Further Sahara.
	
	Test me with "x sun / get sun / n / x sun / n / x sun / tie rope to the sun".
	
...where the response here behaves as though the sun is in reach. If we had a fully implemented tying action, the player would (even more disastrously) be allowed to lasso celestial objects.

We could add a second instead rule as well:
	
	{*}"Waterworld 3"

	A view is a kind of backdrop. 

	Instead of doing something other than examining when the noun is a view:
		say "You are too far from [the noun] to do anything but look."
	Instead of doing something other than examining when the second noun is a view:
		say "You are too far from [the second noun] to do anything but look."

	The player carries a rope.

	The sun is a view. It is everywhere. The description is "A blazing sun makes you wish you had never been born."

	The Sahara is a room. North of the Sahara is More Sahara. North of More Sahara is Yet Further Sahara.

	Test me with "x sun / get sun / n / x sun / n / x sun / tie rope to sun".

This produces acceptable output again, but there is a more elegant way, one that works better with Inform's existing world model. Currently the default model assumes that accessibility -- whether the player can reach something or not -- is checked between the Before... rules and the Instead... rules. We can add our own accessibility rules, including this one to govern whether views are accessible. So for instance:

	{*}"Waterworld 4"

	A view is a kind of backdrop. 

	The can't touch views rule is listed before the access through barriers rule in the accessibility rulebook.

	Accessibility rule (this is the can't touch views rule):
		if the action requires a touchable noun and the noun is a view:
			say "You are too far from [the noun] to do anything but look." instead;
		if the action requires a touchable second noun and the second noun is a view:
			say "You are too far from [the second noun] to do anything but look." instead; 

	The player carries a rope.

	The sun is a view. It is everywhere. The description is "A blazing sun makes you wish you had never been born."

	The Sahara is a room. North of the Sahara is More Sahara. North of More Sahara is Yet Further Sahara.

	Test me with "x sun / get sun / n / x sun / n / x sun / tie rope to sun".

Now our new accessibility rule fits into its proper stage.