When set to 1, this option indicates that the input system is homogenized and the output should be given in projective space.
i1 : R = CC[x,y,z];
i2 : f = {(x^2+y^2-z^2)*(z-x),(x^2+y^2-z^2)*(z+y)};
i3 : bertiniPosDimSolve(f,IsProjective=>1);
The object IsProjective is a symbol.