as 是一个多词性多词义的词汇,你所列出的例句中的 as 是代词,用来指代前述的或要提到一个事实,意思是 “上述的这一点” 或 “正如后面要提到的这一点”.语法上把它归类为关系代词.与其他关系代词不同的是,as 指代的是一个句子或一个短语,而不是一个先行词；as 引导的从句不仅可以作非限制性定语从句,还可以用作表语从句.你所列举的句子多数是后一类.
用作非限制性定语从句
The full text reads as follows.
—as指代the fulltext.
As is well known,we love peace and hate invasion.众所周知,我们热爱和平,憎恨侵略.
—as指代we lovepeace and hate invasion
用作表语从句
Things are not always as they seem to be
—as指代things arenot always (like that),因此可改写为things are not always like that which they seem to be
Every idea we have is as it were copied from what we sense orexperience.（as it were 表示虚拟语气）
—as 指代Every ideawe have,可以改写为Everyidea we have is like that which we have were copied from what we sense orexperience
I am as I was
—as 指代I am like that,可改写为 I am like that which I was.
Perhaps that is as it should be for a film set in Iraq.
—as指代that is,可改写为Perhaps that is like that which should be for a film set in Iraq.
That's just as it should be.理当如此
—as 指代 That'sjustlike that which should be
事实上,“as it + 系动词”已经是一种习惯用法,因此上面的改写都是多余的.
as it is 照现在的样子
as it was 一如既往
as it seem to be 正如看起来的样子、
as it should be 正如本来的那样