英语句子结构分析!牛津高阶第八版,compact adj.smaller than is usual for thing

(The size of something) is smaller than (the size of one thing) is usual for things of the same kind.
省略句式,省略了主句和比较从句的主语.
than,连词之后是省略主语后的谓语动词is,表语usual for the things of the same kind.
感觉上面,以size为例做主语,有些不太恰当,或者过于具体.
smaller than is usuall for things of the same kind,就是个比较句型中主句的主语,谓语,从句的主语被省略掉了.主句的主语,是某物; 从句的主语应该是形式主语it,.
如果,我们说,This computer is smaller than it is ususal for comeputers.it 代表人们现有认识到的某种物品的大小结构特点的标准.
我们可以用compact,这个词来描写this computer.