Dealer in textile fabrics (6)
(Other definitions for draper that I've seen before include "Fabric seller" , "Retailer of fabrics" , "Seller of textiles" , "He sells fabrics" , "Cloth merchant" .)
'dealer in textile fabrics' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mercer that I've seen before include "Textile dealer (historical)" , "Old tradesman" , "Dealer in textile fabrics" , "Dealer in textiles or dry goods" , "Dealer in fine cloth" .)