( Macro Names

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 7.2 Macro Names
 All of the Autoconf macros have all-uppercase names starting with `AC_'
 to prevent them from accidentally conflicting with other text.  All
 shell variables that they use for internal purposes have
 mostly-lowercase names starting with `ac_'.  To ensure that your macros
 don't conflict with present or future Autoconf macros, you should
 prefix your own macro names and any shell variables they use with some
 other sequence.  Possibilities include your initials, or an abbreviation
 for the name of your organization or software package.
    Most of the Autoconf macros' names follow a structured naming
 convention that indicates the kind of feature check by the name.  The
 macro names consist of several words, separated by underscores, going
 from most general to most specific.   The names of their cache
 variables use the same convention ( Cache Variable Names, for
 more information on them).
    The first word of the name after `AC_' usually tells the category of
 feature being tested.  Here are the categories used in Autoconf for
 specific test macros, the kind of macro that you are more likely to
 write.  They are also used for cache variables, in all-lowercase.  Use
 them where applicable; where they're not, invent your own categories.
      C language builtin features.
      Declarations of C variables in header files.
      Functions in libraries.
      UNIX group owners of files.
      Header files.
      C libraries.
      The full path names to files, including programs.
      The base names of programs.
      Definitions of C structures in header files.
      Operating system features.
      C builtin or declared types.
      C variables in libraries.
    After the category comes the name of the particular feature being
 tested.  Any further words in the macro name indicate particular aspects
 of the feature.  For example, `AC_FUNC_UTIME_NULL' checks the behavior
 of the `utime' function when called with a `NULL' pointer.
    A macro that is an internal subroutine of another macro should have a
 name that starts with the name of that other macro, followed by one or
 more words saying what the internal macro does.  For example,
 `AC_PATH_X' has internal macros `AC_PATH_X_XMKMF' and
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