7. Format of acconfig.h

acconfig.h is used to generate config.h.in, which is the file used to generate config.h.
It should contain all the macro definitions needed to control the program.
In it, a line of #undef MYMACRO specifies that the macro should not be defined by default. If it was defined during the run of the ./configure script, it would replace it as such.
A line containing #define MYMACRO specifies that the macro would always be defined, but its value may vary.
The utility autoheader can help in creating an initial config.h.in file.