在Solr SynonymFilterFactory中使用expand = true？

Question

Solr doc解释了expand = true在SynonymFilterFactory中的作用如下：

a synonym will be expanded to all equivalent synonyms. 
If it is false, all equivalent synonyms will be reduced to the first in the list. 

我想知道它究竟意味着什么？如果有人可以详细说明它的作用，那就太棒了。

Answer 1

来自Solr Wiki上的Solr SynonymFilterFactory文档：

 # If expand==true, "ipod, i-pod, i pod" is equivalent to the explicit mapping:
 ipod, i-pod, i pod => ipod, i-pod, i pod

 # If expand==false, "ipod, i-pod, i pod" is equivalent to the explicit mapping:
 ipod, i-pod, i pod => ipod