AUTOCAD参数约束功能

概要：http://through-the-interface.typepad.com/through_the_interface/2011/08/a-simplified-net-api-for-accessing-autocad-parameters-and-constraints.html

demo：http://adndevblog.typepad.com/autocad/2012/03/working-with-associative-parameters-from-api.html

学习视频：http://through-the-interface.typepad.com/through_the_interface/2010/08/devtv-on-autocad-2011s-associative-surfaces-api.html