[Discuss-gnuradio] Packet Header Generator - how it works?

[Miguel Santos]

Hi all,
I want to add a preamble to my data and I started to explore the 
"tx_ofdm.grc" example, but I have no idea on what to use on "Formatter 
Object" attribute from Packet Header Generator. Can anyone explain it to 
me?
I'm trying here 
(https://gnuradio.org/doc/doxygen/classgr_1_1digital_1_1packet__headergenerator__bb.html)
 
but still can't get it.

Thanks,
Miguel