Backward loop increase purlwise

I’m working on this sweater pattern where the instructions state that on the left front piece I’m suppose to increase using the backward loop method (where the increases take place on the RS of the st st). Then on the right front piece I’m suppose to make the same increases on the WS (purl rows), but I can’t quite figure out how to do a backward loop increase purlwise. Any advice??

I don’t think you have to worry about making it any other way than the usual way. The loop is neither a knit or a purl and the way you work it will be what it becomes. IOW just do it, and then either knit it or purl it as needed.