[Asterisk-Users] Undocumented "exten" syntax?

[Sean Kennedy]

John Goerzen wrote:

>Over at http://www.voip-info.org/wiki-Asterisk+tips+911, I see these
>extensions.conf lines:
>
>exten => s,1,SetVar(SET_EMERG_FLAG=0)
>exten => s,n(checkavail),ChanIsAvail(${EMERGENCY_TRUNK})
>exten => s,n,SetGlobalVar(EMERGENCY=1)
>exten => s,n,SetVar(SET_EMERG_FLAG=1)
>exten => s,n(dial),Dial(${EMERGENCY_TRUNK}/${EMERGENCY_NUM})
>exten => s,s+2(trunkbusy),GotoIf($[${EMERGENCY} = 1]?inprogress)
>
>Now, I have several questions:
>
> * What is the "n" priority and how can they use it for several
>   different items?  Don't they need an increasing integer there?
>
> * What is the "(checkavail)" doing?
>
> * What does "s+2" mean?
>
>I've tried looking in docs and the wiki but can't figure it out.
>
>Thanks!
>
>-- John
>
I have been curious about this as well.  I was thinking it may be pseudo 
code?  It seems easy enough to read, so that may be what it is. 

*shrug* I'd like to know the answer to this as well.

Sean