When converting cube luts to presets, what does the expand gamut option do?

When converting a lut to a preset there are two options for gamut , clip and expand. I understand what clip does , but I was curious exactly what expand does and how it works. I assume it stretches luts encoded in smaller color spaces to cover prophoto's gamut.  However, I've made both clipped and expanded ones and never see any difference in appearance or the histogram on raw files even with images with overexposed or highly saturated areas.