The Jargon File (version 4.4.7, 29 Dec 2003):

RTFS
 /R?T?F?S/

    [Unix]

    1. imp. Abbreviation for ?Read The Fucking Source?. Variant form of RTFM,
    used when the problem at hand is not necessarily obvious and not answerable
    from the manuals ? or the manuals are not yet written and maybe never will
    be. For even trickier situations, see RTFB. Unlike RTFM, the anger
    inherent in RTFS is not usually directed at the person asking the question,
    but rather at the people who failed to provide adequate documentation.

    2. imp. ?Read The Fucking Standard?; this oath can only be used when the
    problem area (e.g., a language or operating system interface) has actually
    been codified in a ratified standards document. The existence of these
    standards documents (and the technically inappropriate but politically
    mandated compromises that they inevitably contain, and the impenetrable 
    legalese in which they are invariably written, and the unbelievably
    tedious bureaucratic process by which they are produced) can be unnerving
    to hackers, who are used to a certain amount of ambiguity in the
    specifications of the systems they use. (Hackers feel that such ambiguities
    are acceptable as long as the Right Thing to do is obvious to any
    thinking observer; sadly, this casual attitude towards specifications
    becomes unworkable when a system becomes popular in the Real World.)
    Since a hacker is likely to feel that a standards document is both
    unnecessary and technically deficient, the deprecation inherent in this
    term may be directed as much against the standard as against the person who
    ought to read it.


The Free On-line Dictionary of Computing (30 December 2018):

RTFS

    1. Read The Fucking Source.  Variant form of RTFM,
   used when the problem at hand is not necessarily obvious and
   not answerable from the manuals - or the manuals are not yet
   written and maybe never will be.  For even trickier
   situations, see RTFB.  Unlike RTFM, the anger inherent in
   RTFS is not usually directed at the person asking the
   question, but rather at the people who failed to provide
   adequate documentation.

   2. Read The Fucking Standard; this oath can only be used when
   the problem area (e.g. a language or operating system
   interface) has actually been codified in a ratified standards
   document.  The existence of these standards documents (and the
   technically inappropriate but politically mandated compromises
   that they inevitably contain, and the impenetrable legalese
   in which they are invariably written, and the unbelievably
   tedious bureaucratic process by which they are produced) can
   be unnerving to hackers, who are used to a certain amount of
   ambiguity in the specifications of the systems they use.
   (Hackers feel that such ambiguities are acceptable as long as
   the Right Thing to do is obvious to any thinking observer;
   sadly, this casual attitude toward specifications becomes
   unworkable when a system becomes popular in the Real World.)
   Since a hacker is likely to feel that a standards document is
   both unnecessary and technically deficient, the deprecation
   inherent in this term may be directed as much against the
   standard as against the person who ought to read it.

   [Jargon File]