Aulixiary frames for window doors

Why Aulixiary frames needed ?
Aulixiary frames installed need measure the hole of the wall first ,then prouce right sixe window/doors match well ,install and removble windows from Auxiliary frame is easy and fast . High quality WPC/PVC aulixiary frame is energy saving, insulation, waterproof and so on.
In China Jiangsu Province ,Jiangsu Provincial Department of Housing and Urban-Rural Development mandatory all external window and doors install aulixiary frames since 1 January 2014 for all civil construction.