嵌入式关系分句

嵌入式关系分句的下定义是：

有一种关系分句(即定语从句)，它既是先行词的后置修饰语(即定语)，同时又是另外一个分句结构的宾语(即宾语从句)”，此分句结构就被嵌入在该定语从句中，即嵌入式关系分句。

例如：

In his breastpocket he had a patch of scarlet, which I suppose was the paper cap serving as a handkerchief.

需要注意两点：

第一，从句which I suppose was the paper cap serving as a handkerchief是patch of scarlet的定语从句。

第二，该定语从句的先行词在patch of scarlet定语从句实际上是充当I suppose的宾语从句的主语的，还原进定语从句并补全省略部分，则有：
I suppose (that) patch of scarlet was the paper cap serving as a handkerchief. 

(that) patch of scarlet was the paper cap serving as a handkerchief是I suppose的宾语从句。
综上所述，当先行词在定语从句中充当的成分是另一个从句（宾语从句）的某个成分时（正常来说，先行词），则我们可以称这个定语从句为嵌入式关系分句，也就是将这个宾语从句嵌入到了定语从句中。