To recap from my previous post: every piece if interactive fiction hasd a space of possibilities. The author can choose to make these possibilities explicit to the player (unveiling them) , or the author can try to hide them (veiling them), relying on hinting, context and inspiration of the player.
This post is going to be very exploratory and prelimenary; I'm going to think aloud, and I invite you to think along with me and comment. What are the techniques used for veiling and unveiling? When is veiling useful, when is unveiling useful? How do the two interact?
I just deleted a list of general pros and cons of veiling and unveiling. We really need to look at concrete situations if we wish to go any further than mere vagueness. (I also just found out that 'vagaries' does not mean 'vague things'.)
The out-in-the-open puzzle
An out-in-the-open puzzle is like a chess problem: the situation is clear, the rules are clear, but the very complexity of the situation is what makes it non-trivial. (I spoke about puzzles of complexity here.) The best example known to me in interactive fiction is the game All Things Devours (sic).
What the author of All Things Devours has cleverly done is this. The first part of the game is a process of discovery, which slowly unveils all the possibilities the player has. At some point, just when things start to become difficult, you understand the rules of the game and thus the possible moves you can make. The puzzle then is to find the right sequence of moves, and this is satisfyingly difficult.
However, there is still some kind of veil in place. Suppose there are ten different ways to fail the game; that is, not ten sequences of moves that lead to failure, but ten different in-game reasons for failure. (Leaving a door open; not getting to place B on time; and so forth.) There is a sense in which only the eleven paths which lead to these ten failures and the one success are meaningfully different actions, even if all of them can be realised through many sequences of micro-actions.
Now the game could have presented us with a list of these eleven sequences, from which we would have to choose the right one. But this would have destroyed all the fun, because having the possibilities spelled out for us thus would allow us to infer the meaning of all the sequences almost instantly, and the puzzle aspect would have been gone.
We are seeing something very complex here. An action like "close the door" can be unveiled in the sense that we understand perfectly that it is possible, and what its effect on the state of the world will be. But on a higher semantic level, we may fail to see what it means in the context of the puzzle. (In the chess problem, we know that 1. Pf6 is possible and we know what it does, but we may fail to see that it is necessary in order to block 4. ... Qe8. And what on earth is the English notation for a knight? I've use the Dutch/German 'P', but that can't be it; nor can it be 'K', because that probably stands for King.)
So what we are doing is unveiling the micro-possibilities by revealing the content and the rules of the world, while keeping the macro-possibilities veiled behind a veil of complexity. (Here micro is defined by the kind of manipulations the player can do, while macro is defined by the logic of the overarching puzzle.)
The hidden-action puzzle
You're walking through a seemingly endless if roofless maze, and the only thing you have to do to escape is type fly - but you won't know you have wings until you take a look at yourself and notice that your physique has changed since you drank the blue potion three scenes ago. (I'm partly making this up.)
In this case, the puzzle is constituted by the fact that the possibility of the action is not apparent. If fly were a verb generally used in interactive fiction (because most PCs could fly), it would be the first thing anyone tried and there'd hardly be a puzzle at all. But since it is not, and since the game does not draw your attention to that fact that you can fly, the possibility remains veiled and there is a puzzle to solve.
For this kind of puzzle, then, veiling is crucial. On the other hand, in order for a solution to be achievable at all, the writer must use one of a variety of techniques to point the reader in the right direction.
One way to do this is by giving the player information that allows his to deduce or at least form the suspicion that he might be able to fly. In this case, drinking the blue potion might print the text "You feel a slow transformation coming over you.", and examining yourself might print "By god - you have grown wings!" Together, these two would give the player a fair chance of guessing that flying is the right option.
Another way to do this is by making the space of possible solutions so small that the player can simply try them all. If your character is falling from a plane without a parachute, flying is about the only possibility. This method has the drawback that only meta-thinking will allow the player to disclose the possibility: the puzzle must be solvable, therefore this action (which seems the only possible solution) must be possible. If one cares about 'crimes against mimesis', one should try to avoid that.
The hidden ideology
Suppose I wish to write a game about violence, and my aim is to show that the player of interactive fiction is predisposed to solving problems in a violent way, implicitly criticising her. (I do not know whether any piece of IF has attempted this, but the meta-RPG Powerkill did.)
The way to implement this is to create situations which can be overcome in both violent and non-violent ways, and not making this explicit. If I give you a problem and say "you can solve it in a violent way, like this, and in a non-violent way, like this", then you are not going to attempt the violent way without ever realising that a non-violent way might also be possible. But if I give you a problem and keep my mouth shut about the possible solutions, you might do just that. And then, at the end of the game, when it suddenly becomes apparent that there were also non-violent solutions, you realise something profound and scary about yourself.
Hiding the uncomfortable/inappropriate
In his review of The Baron David Whyld wrote:
While it’s possible, as I discovered after numerous runs through the game, to reach an ending that doesn’t involve the player having to carry out some pretty distasteful actions, it’s still a little disturbing that such actions *are* possible in the game. Maybe I'm just perverse, but the first action I tried when discovering Maartje in her room was one I felt would either not be recognised, or I’d be told off for even attempting such a thing, but the game did neither. It went ahead with what I’d typed, and then did all the other unpleasant and distasteful things as well. I suppose it’s my own fault for typing the commands in the first place, and I can hardly get indignant over it considering it was my option to type those things, but at the same time part of me wonders how necessary this unpleasant aspect of the game was.Whatever one believes about the necessity of including this uncomfortable content at all, one can hardly disagree that veiling the possibility of doing these distasteful action was necessary. The disturbing content is there for those who wish to explore the very blackest consequences of the game's premise; but there are many who do not wish to take their exploration that far, and for them, even knowing that it is there (but certainly having it pointed out to them by the piece that they are now in a position to unlock it) can be too much.
We can also see this kind of veiling in less dramatic contexts. If there is a game in which you can play in either a very friendly or a very unfriendly way, then it may be the right design decision to veil these dual possibilities so that the person playing the PC friendly isn't constantly made aware of the possibility of playing in a very unfriendly way.
These four cases certainly do not exhaust the topic, but they may serve as a starting point.