such as引导同位语时as是什么词性？

such as表示举例，做同位语时，意为“例如，诸如此类的，像……那样的”，相当于like或for example。如：

There are few poets such as Keats and Shelly. 像济慈和雪莱这样的诗人现在很少了。

Adverbs are used to modify verbs, such as Keats and Shellych as “quickly” in “she ran fast”. 副词用来修饰动词，例如“她跑得快”中的“快”。

Animals such as rabbits and deer continue to be active all winter，finding food wherever they can . 像兔和鹿这样的动物整个冬天都是很活跃的，它们到处寻找食物。

such as引出同位语有下面几点用法：

(1) 这类结构既可表现为“名词+such as+例子”，也可表现为“such+名词+as+例子”。如：

I enjoy songs such as this one.= I enjoy such songs as this one. 我喜欢像这首歌一样的歌。

(2) 若后接动词，通常用动名词，有时也可用动词原形。如：

Don’t do anything silly such as marry him. 不要做什么蠢事，比如说去嫁给他。

Magicians often perform tricks such as pulling a rabbit out of a hat. 魔术师常常变从帽子里抓出兔子的戏法。

问题：1.当such as引导同位语时，as是关系代词吗？比如下面这句：

English is spoken in many countries,such as Australia and Canada.许多国家都讲英语,例如澳大利亚和加拿大.

能否将as当做关系代词并将原句完整表达为：

English is spoken in many countries,such as are Australia and Canada.

即as在从句中做主语。 

2.前面的例子中出现过as后面跟句子的情况，比如such as marry him 和 such as pulling a rabbit out of a hat，这是不是说明such as引导同位语时as是连词？

3.但是例子中也出现过 such as Keats and Shelly同位语，这个看起来似乎as是介词，搞不清楚such as引导同位语时，as到底是什么词性了。