继续翻译
The double-colon rules for a target are executed in the order they appear in the makefile. However, the cases where double-colon rules really make sense are those where the order of executing the recipes would not matter. Double-colon rules are somewhat obscure and not often very useful; they provide a mechanism for cases in which the method used to update a target differs depending on which prerequisite files caused the update, and such cases are rare. Each double-colon rule should specify a recipe; if it does not, an implicit rule will be used if one applies. *Note Using Implicit Rules: Implicit Rules.
对一个目的双冒号规则，执行顺序是它们在makefile中出现的顺序。但是，双冒号规则真正有益处的场合是执行顺序没有影响的哪些。
双冒号规则有些模糊不清，而且也不是很有用；它们提供了一种机制，这可以使得在改变目的所用的方法依赖于具体由哪些前提条件触发的场合很适用，但毕竟这种情况很少见。
每个双冒号规则应当指定一个片段；如果不这样做，一个隐式规则将会被适用。*Note Using Implicit Rules: Implicit Rules.
后文待续