[Asterisk-Users] Using SIP_HEADER() Function correctly

[Rushowr]

(oops, wrong account, let's try again, without the work email getting it
blocked)

Am I correct in my thought that if I was to issue:

Exten = 1234,1,VERBOSE(1|${SIP_HEADER(HEADERNAME)})

In the dialplan that asterisk would return the value of the HEADERNAME
field, if there was one attached to the invite?

I've been hunting around, but have found no working examples of this. 

Thanks

SKM