It’s called CBOTDEBUGDD() and currently just returns an empty string. It’s not highlighted in the editor, just like produce(). This was probably used during CBOT engine development for testing.

extern void object::Program()
{
message(CBOTDEBUGDD());
}

Related part of Colobot: Gold Edition source code:
src/CBot/CBotProgram.cpp:1031-1047
src/CBot/CBotProgram.cpp:1105