undocumented feature

undocumented feature
 n.

   See {feature}.
    

feature
undocumented feature

   <jargon> 1. A good property or behaviour (as of a program).
   Whether it was intended or not is immaterial.

   2. An intended property or behaviour (as of a program).
   Whether it is good or not is immaterial (but if bad, it is
   also a {misfeature}).

   3. A surprising property or behaviour; in particular, one that
   is purposely inconsistent because it works better that way -
   such an inconsistency is therefore a {feature} and not a
   {bug}.  This kind of feature is sometimes called a {miswart}.

   4. A property or behaviour that is gratuitous or unnecessary,
   though perhaps also impressive or cute.  For example, one
   feature of {Common LISP}'s "format" function is the ability to
   print numbers in two different Roman-numeral formats (see
   {bells, whistles, and gongs}).

   5. A property or behaviour that was put in to help someone
   else but that happens to be in your way.

   6. A bug that has been documented.  To call something a
   feature sometimes means the author of the program did not
   consider the particular case, and that the program responded
   in a way that was unexpected but not strictly incorrect.  A
   standard joke is that a bug can be turned into a {feature}
   simply by documenting it (then theoretically no one can
   complain about it because it's in the manual), or even by
   simply declaring it to be good.  "That's not a bug, that's a
   feature!" is a common catch-phrase.  Apparently there is a
   Volkswagen Beetle in San Francisco whose license plate reads
   "FEATURE".

   See also {feetch feetch}, {creeping featurism}, {wart}, {green
   lightning}.

   The relationship among bugs, features, misfeatures, warts and
   miswarts might be clarified by the following hypothetical
   exchange between two hackers on an airliner:

   A: "This seat doesn't recline."

   B: "That's not a bug, that's a feature.  There is an emergency
   exit door built around the window behind you, and the route
   has to be kept clear."

   A: "Oh.  Then it's a misfeature; they should have increased
   the spacing between rows here."

   B: "Yes.  But if they'd increased spacing in only one section
   it would have been a wart - they would've had to make
   nonstandard-length ceiling panels to fit over the displaced
   seats."

   A: "A miswart, actually.  If they increased spacing throughout
   they'd lose several rows and a chunk out of the profit margin.
   So unequal spacing would actually be the Right Thing."

   B: "Indeed."

   "Undocumented feature" is a common euphemism for a {bug}.

   7. An attribute or function of a {class} in {Eiffel}.

   [{Jargon File}]

   (1995-10-22)