+_UNSUPPORTED_MESSAGE= ${OPSYS} version you are running is not supported by the Ports Collection, no port is guaranteed to build. Please upgrade to a supported release or, as a last resort, use a ports tree snapshot dated within your system support lifetime.
+. if defined(ALLOW_UNSUPPORTED_SYSTEM)
+WARNING+= "${_UNSUPPORTED_MESSAGE}"
+. else
+IGNORE= ${_UNSUPPORTED_MESSAGE} You may define ALLOW_UNSUPPORTED_SYSTEM to proceed, but you have been warned