While a call log is going to be required, you could calm down and actually look at the code as I mentioned.
Now that I am at home, I did. It is very clear in the code what is happening. Here is the dial plan generated on my system.
[park-return-routing]
include => park-return-routing-custom
exten => 720,1,Set(PLOT=720)
exten => 720,n,ExecIf($[${LEN(${PREPARK_CID})} = 0]?Set(PREPARK_CID=${CALLERID(name)}))
exten => 720,n,Set(CALLERID(name)=${PARKINGSLOT}:${PREPARK_CID})
exten => 720,n,ExecIf($["${ALERT_INFO}"!=""]?Set(HASH(__SIPHEADERS,Alert-Info)=${ALERT_INFO}))
exten => 720,n,ExecIf($["${RVOL}"!=""]?Set(HASH(__SIPHEADERS,Alert-Info)=${ALERT_INFO}\;volume=${RVOL}))
exten => 720,n,Dial(${PARKCALLBACK},15,b(func-apply-sipheaders^s^1),tr)
exten => 720,n,Set(PARKCALLBACK=)
exten => 720,n,Goto(ext-local,vmi103,1)
exten => 721,1,Goto(720,1)
exten => 722,1,Goto(720,1)
exten => 723,1,Goto(720,1)
exten => 724,1,Goto(720,1)
exten => 725,1,Goto(720,1)
;--== end of [park-return-routing] ==--;
It is a Dial command exten => 720,n,Dial(${PARKCALLBACK},15,b(func-apply-sipheaders^s^1),tr)
PARKCALLBACK is set in [macro-park-call]
to PARKER
exten => s,n,Noop(PARKRETURNTO: ${SHARED(PARKRETURNTO,${CHANNEL})})
exten => s,n,Park(${ARG2},sc(${CONTEXT},s,200))
exten => s,1+199(backtosender),Noop(Attempting to go back to sender)
exten => s,n,Set(PARKCALLBACK=${PARKER})
exten => s,n,Set(SHARED(PARKRETURNTO,${CHANNEL})=)
exten => s,n,Goto(park-return-routing,${PARKINGSLOT},1)
But I don’t know where PARKER comes from with a quick look, as that is the only reference.
[jbusch@pbx ~]$ sudo grep PARKER /etc/asterisk/*.conf
/etc/asterisk/extensions_additional.conf:exten => s,n,Set(PARKCALLBACK=${PARKER})
[jbusch@pbx ~]$