Rather than mechanical implementation, discourse should be thought of as the creative extension-through-combination of existing resources, with conventional cases of a discourse drawing upon a single discourse type as in the interview extract being thought of as limiting cases rather than the norm.

对于with结构我的理解是：with conventional cases of a discourse drawing upon a single discourse type. 红色部分是修饰conventional cases，但是 as后就看不明白了，希望老师指点一下。