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§18.9. Deciding the concealed possessions of something
1. When it happens. Frequently - whenever Inform needs to check whether something is visible or not. Nothing should be printed, and the activity needs to run quickly, so it should not (for instance) calculate best routes through complicated maps before getting an answer.
2. The default behaviour. There is no concealment. The ordinary rules still apply, though: the contents of a closed opaque container are invisible because there is a barrier in the way which cannot be seen through, even though nobody is "concealing" anything.
3. Examples. To repeat a number of brief examples given at the end of Chapter 3, where this activity made an early appearance:
Rule for deciding the concealed possessions of the Cloaked Villain: if the particular possession is the sable cloak, no; otherwise yes.
The coin is in the Roman Villa. The face and inscription are parts of the coin. Rule for deciding the concealed possessions of the coin: if the coin is carried, no; otherwise yes.
The value "particular possession" is the one whose concealment is in question, of course. We can ignore this if someone is invariably secretive:
Rule for deciding the concealed possessions of the furtive ghost: yes.
In general a rule for deciding the concealed possessions of something will decide "yes" if finishes without making a decision, but it's better style to write such a rule in such a way that it always makes a decision.
