二个语法结构之间的关系，除了并列、修饰/限制之外，还可能是补充。例如：

I like sports and music. music和sports为并列关系。

I like sports that have a fast pace. that从句与sports为修饰/限制关系。

I like sports, such as football. such as football与sports为补充关系。

《剑桥语法》把这种补充关系的语法结构称为补充语supplement。补充语可以是对名词的补充说明，也可以是对其他词或词组甚至整个句子的补充说明。所以补充语包含了传统语法的非限制性定语、非限制性同位语、非谓语动词作状语、插入语、以及部分传统语法难以分类的句子成分。

补充语前通常用逗号，但也可以用破折号。可以带标记词such as, for example, that is, 等，也可以不带标记词。

我认为，在传统语法中引入补充语这个术语来解释一些难以分类的句子成分是有帮助的。例如在 I like sports, such as football. 这个句子中，such as football显然不是同位语。分析为插入语，则过于笼统。如果分析为sports的补充语，则简洁明了。

This conflict was the latest symptom of a revenge plan, of the sort that has led to many accidents in other places.

of the sort that has led to many accidents in other places 为前面介词短语of a revenge plan的补充语，对其作补充说明。由于二个of介词短语补充关系，不是并列关系，所以不能用并列连词and.

His death gives Burundi a chance to tackle the pandemic—and, perhaps, of a bit less foul play.

本句的破折号提示后面部分为补充语（补充语偶尔可以用and). 对前面名词a chance作补充说明。——and, perhaps, (a chance) of a bit less foul play.

Statues become flashpoints at times of social change because they honour the values, and reflect the hierarchies, of the times in which they were erected.

这个句子不同于以上二句。because从句主语后接二个谓语动词，二个谓语动词的宾语共用of the times...介词宾语，为了简洁，第二个谓语的宾语省略了其后的定语，前移插入第一个动词的宾语与其定语之间，表示二个名词的定语相同。原来的修饰关系如下：

Statues become flashpoints at times of social change because they honour the values of

the times in which they were erected and they reflect the hierarchies of the times in which they were erected.

再看一个类似结构：

Tom is as tall as, or even taller than, John.