The foot can be set to sew on each side of the zipper. The edge of the foot guides the zipper to ensure straight placement. The AcuFeed mechanism is great for zippers in thin or stretchy fabrics; it feeds all the layers through evenly for a polished look. 

Janome 
MC12000 Horizon Memory Craft, MC14000 Horizon Memory Craft, MC15000 Horizon Memory Craft, MC8200QC, MC8200QCPSE, MC8200QCLE, MC8900QC, Skyline S7