Indicates if parameters to a Function or Sub are passed by reference as with Byref, or by value as with Byval by default when the by value / by reference specifier is not explicitly stated.

__FB_OPTION_BYVAL__ is set to non-zero (-1) if by default parameters are passed value, and zero (0) if by default parameters are passed by reference.

The default for passing parameters by reference or by value is determined by the -lang command line option used during compilation or usage of Option Byval in the source file.