Source : Free On-Line Dictionary of Computing

If you want X, you know where to find it.
     
         There is a legend that {Dennis Ritchie},
        inventor of {C}, once responded to demands for features
        resembling those of what at the time was a much more popular
        language by observing "If you want {PL/I}, you know where to
        find it."  Ever since, this has been hackish standard form for
        fending off requests to alter a new design to mimic some older
        (and, by implication, inferior and {baroque}) one.  The case X
        = {Pascal} manifests semi-regularly on {Usenet}'s
        {news:comp.lang.c} {newsgroup}.  Indeed, the case X = X has
        been reported in discussions of graphics software (see {X
        Window System}).
     
        [{Jargon File}]
     
        (1995-10-25)