as引导的从句如何理解

The enrollment ofa prospective pupil to the School is subject to the School's Admissions andEntry policies and other policies and procedures as modified by the School from time to time.

请问这句话的as引导的从句如何理解？

The enrollment ofa prospective pupil to the School is subject to the School's Admissions andEntry policies and other policies and procedures as modifiedby the School from time to time.

as 从句不完整，modified 是过去分词。黑体部分作 policies and procedures 的定语。

这种省略 be 的 as + 过去分词短语，常用来作定语或状语。以 as stated 为例：

His secondstatement agrees with facts as stated by the other witnesses.（作定语）

他的第二份供述与其他目击证人所陈述的事实相符。

《柯林斯高阶英汉双解学习词典》

The result of theinvestigation was reported as stated above. （作方法状语）

现将调查结果报告如上。

《汉英大词典》

As is statedabove, this principle applies to all cases. （引导非限制性定语从句）

如前文所述，这一原则合适所有案例。