tcp::payload question

hi,dear irule

 

1:if I use tcp::collect 50 to collect first 50 bytes,then I wanna extract 21-22 bytes via tcp::payload

 

how to achieve this?

 

 

 

2:tcp::payload 2 means take first 2bytes from payload,right?

 

 

3:in the tcp::payload size

 

Returns the accumulated TCP data content. If is specified, and more than bytes are available, only the first bytes of collected data are returned.

 

 

what does "If is specified, and more than bytes are available, only the first bytes of collected data are returned If is specified, and more than bytes are available, only the first bytes of collected data are returned" mean?