As can be seen from是什么语法？是非限制性定语从句么

As can be seen from是什么语法？是非限制性定语从句么

这是非限制性定语从句。
as引导的非限制性定语从句，可以用来指代整个主语或主语的一部分内容，在这种情况下，as和which有时可以交换使用，有时又不可以交换，as引导的非限制性定语从句可放句首，which引导的从句不可以。
as引导的非限制性定语从句，对主句的内容起积极的作用，反之则应用which．使比较：
Mother gave him some money, as was a pleasure to him．
母亲给他些钱，这使他很高兴。
Mother gave him some advice, which made him unhappy．
母亲给他提了点建议，这使他很不高兴．
关系代词as强调as前面整个句子的内容，which强调从句内容。如：
Her speech was wonderful, as we had expected．
正如我们所期盼的那样，她的发言棒极了。
His father died, which made him very sad．
他父亲去世了，这使他很悲伤。
在非限制性定语从句中，谓语是连系动词be时，常用as作主语，而谓语是实义动词时，则用which作主语。如：
Tom is late for class, as is often the case．
汤姆迟到了，他往往是这样。
Bamboos are hollow, which makes them very light．
竹子是空心的，这使它们重量很轻。
as引导的非限制性定语从句要与主句语义一致。如果主句为肯定句，从句用否定句，则一般用which引导。如：
Mr. Johnson is a teacher, as is clear from his manner．
约翰逊先生是位教师，这从他的举止可以看出来。
He has to work on Sundays, which he doesn’t like．
他必须在星期天工作，他不喜欢这样。
as含有“正如……”的意思，常与表示“判断、了解，指出”等意思的动词连用，作这些动词的宾语，或该动词用被动语态，as作主语。
She believed the fact, as had been expected．（as作主语）
As we know now, bats come out only at night．（as作宾语）

例句： 1 As can be seen from his accent，Mr. Smith is from Scotland. 里面，As can be seen from his accent是插入语结构。 2 Mr. Smith is from Scotland ， which can be seen from his accent 这一句里面，which can be seen from his accent 是定语从句部分。 3 That Mr. Smith is from Scotland can be seen from his accent 这里 ，that引导的句子是主语从句。 4 Mr. Smith‘s being from Scotland can be seen from his accent 这里，Mr. Smith‘s being from Scotland 是动名词结构。动名词结构做主语。