打印设置中的[duplex]选项含义

在打印机配置的DeviceMode中有一个属性：duplex
这个属性有以下几种：Vertical，Horizontal，Simplex
请问分别表示什么含义，有什么功能区别？

看看MSDN就可以了
dmDuplex：Selects duplex or double-sided printing for printers capable of duplex printing. Following are the possible values。
DMDUP_SIMPLEX:Normal (nonduplex) printing.
DMDUP_HORIZONTAL:Short-edge binding, that is, the long edge of the page is horizontal. 
DMDUP_VERTICAL:Long-edge binding, that is, the long edge of the page is vertical.