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A general description is here.
Header ‘R_ext/Rboolean.h’ now defines the type ‘Rboolean’ as an alias
of the standard C type ‘bool’ in C23 mode.
Before release C++ ‘bool’ will be used if the header is included from C++.
The macro ‘_R_RBOOLEAN_IS_BOOL_’ is defined where ‘Rboolean’ is implemented _via_ ‘bool’.
[Deferred pending further testing.]