I got a bit frustrated and ended up searching the source for â[\w]opt[[:upper]]â to find all NativeBoost options. Some of those options are in fact undocumented: optMayGC optProxyLabels optCdecl optReturnNullAsNil optStdcall optNonMovable optReserveCallgateSpace optDebug optNoAlignment optEmitCall optNoCleanup optCheckFailOnEveryArgument optStringOrNull WinUnicode NBFFICallout>>defaultOptions documents most options but refers to NBFFICallout>>allOptions, wich does not exist. Most of the above options can be considered internal, I guess, but the one option I needed (âoptStringOrNullâ) isnât documented anywhere. I had to step through the execution to find out why my function call wasnât working (because I was trying to use âoptCoerceNilToNullâ and didnât know that strings need a special option). Iâd be very thankful if these options would be included in the documentation. Note: âWinUnicodeâ is used by the Windows code in a couple of places, even though the option name is not valid, according to NBNativeCodeGen>>parseOptions: Cheers, Max