This macro expands by default to
64. For a C++
standard conforming preprocessor, the end-user can change this to
128 or 256 by defining this macro to either value before including
any library headers. If the end-user changes the value of the
macro the
BOOST_PP_LIMIT_VARIADIC
macro is changed to the same value unless the end-user has changed
BOOST_PP_LIMIT_VARIADIC to a higher value.