这样录制下来的脚本会长很多。Google suggest的AJAX行为被分别录制成一个个的web_url请求，并且放在web_concurrent_start和web_concurrent_end之间。关于web_concurrent_start函数的描述，可以参考LR帮助文档：
The web_concurrent_start function marks the beginning of a concurrent group. All functions within the group are executed concurrently. The end of the group is marked by the web_concurrent_end function. Within the concurrent group, you may include Action functions and several Service functions.
Note that the functions included within the concurrent group are not executed immediately. Instead they are registered for concurrent execution. When the concurrent group is closed, all of the functions registered as concurrent are executed together.
Concurrent中的函数都会先注册，而不是马上执行，直到web_concurrent_end才一起执行，这个从回放的日志也可以看出来：
Action.c(73): web_concurrent_start was successful [MsgId: MMSG-26392]
Action.c(75): Registering web_url("toolbar_animation_20090618.png") was successful [MsgId: MMSG-26390]
Action.c(83): Registering web_url("search") was successful [MsgId: MMSG-26390]
Action.c(91): Registering web_url("search_2") was successful [MsgId: MMSG-26390]
Action.c(99): Registering web_url("search_3") was successful [MsgId: MMSG-26390]
Action.c(107): Registering web_url("search_4") was successful [MsgId: MMSG-26390]
Action.c(115): web_concurrent_end was successful, 8506 body bytes, 1355 header bytes, 84 chunking overhead bytes [MsgId: MMSG-26385]
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