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Unix programmers inherit a strong bias toward making interfaces expressive and configurable. Like programmers from other traditions, they think about how to match their interfaces to the target audience — but they differ in how they deal with uncertainty about that target audience. Software developers whose experience is primarily with client operating systems default toward making interfaces simple; they are willing to sacrifice expressiveness to gain ease. Unix programmers default toward making interfaces expressive and transparent, and are more willing to sacrifice ease to get these qualities.

The results of this attitude have often been described as interfaces written “by programmers, for programmers”. But this oversimplifies the matter in an important way. When a Unix programmer opts for configurability and expressiveness over ease, he is not necessarily thinking of his audience as consisting solely of other programmers; rather, he is often acting on a gut-level instinct that in the absence of knowledge about end-users' intentions it is best not to patronize or second-guess them.

The downside of this attitude (which is a close cousin to “mechanism, not policy”) is a tendency to assume that when the highly configurable and expressive interface is done, the job is finished... even if the result is almost impossible for anyone else to use without lengthy study. The flip side of configurability is an urgent need for good defaults and an easy way to set everything to the default. The flip side of expressivity is a need for guidance — be it in the program or the documentation — on where to get started and how to achieve the most commonly-desired results.

-- Henry Spencer

The Rule of Transparency also has an influence. When a Unix programmer is writing to meet an RFC or other standard that defines a set of control options, he tends to assume that his job is to provide a complete and transparent interface to all of those options; whether or not he thinks any given one will actually be used is secondary. His job is mechanism; policy belongs to the user.

This mindset leads to a much stricter attitude about what constitutes standards conformance, one in which incomplete support is much less tolerable. In cases where a Macintosh or Windows developer would say “We don't need to support that feature of the standard; most users won't care, and it's too complicated for them”, a Unix developer is likely to say “We don't know that nobody will ever want this feature or option, therefore we must support it”.

These attitudes can lead to clashes when a Unix programmer is working with others, who are likely to interpret his design choices as a blithe willingness to burden users with technical details that are obscure, pointless, and even frightening. Mac or Windows programmers fear scaring away the many to serve the advanced needs of the few.

The Unix programmer, on the other hand, is likely to see defaulting away from expressiveness as a sort of cop-out or even betrayal of future users, who will know their own requirements better than the present implementer. Ironically, though the Unix attitude is often construed as a sort of programmer arrogance, it is actually a form of humility — one often acquired along with years of battle scars.

The extent to which the Unix attitude is appropriate varies. Whichever side of this divide you the reader are on, it is wise to learn to listen to the other, and wise to understand the premises behind the opposing point of view. Rather than falling into the trap of either intimidating users or condescending to them, it may be possible to build transparent interfaces in which the advanced features are present but inconspicuous. The audacity and kmail case studies in Chapter═6 are good examples to follow.

Finally, a note about user-interface design for nontechnical end-users. This is a demanding art, and Unix programmers don't have a tradition of being very good at it. But with the ideas we've developed from examining the Unix tradition, it is possible to make one strong and useful statement about it. That is: when people say a user interface is intuitive, what they mean is that it (a) is discoverable, (b) is transparent in use, and (c) obeys the Rule of Least Surprise.[107] Of these three rules, Least Surprise is the least binding; initial surprises can be coped with if discoverability and transparency make longer-term use rewarding.

The user interfaces of today's cellphones (for example) have relatively high mnemonic load in that you have to maintain at least a rough mental map of the interface menus to use them rapidly without constantly having to spend attention on checking where you are in the hierarchy. But the better-designed ones rapidly become ‘intuitive‘ for their users anyway, because they have these three qualities.

Intuitiveness is not quite the same quality as ease, because (as the cellphone example shows) people can develop what they think of as ‘intuitions‘ about transparent interfaces that have fairly high mnemonic load, as long as simple operations are easy and there is a discovery path that allows them to assimilate the interface's more difficult corners one step at a time.

[107] This insight comes to us from a nontechnical end-user who just happens to be the author's wife Catherine Raymond.

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