格式：

(1) VCL files start with vcl 4.0;

(2) //, # and / foo / for comments;

(3) Subroutines are declared with the sub keyword; 例如sub vcl_recv { …}；

(4) No loops, state-limited variables（受限于引擎的内建变量）；

(5) Terminating statements with a keyword for next action as argument of the return() function, i.e.: return(action)；用于实现状态引擎转换；

(6) Domain-specific;