[aprssig] HAMFEST objects on APRS!

[Steve Noskowicz]

With the talk of APRS symbols, I'm confused...

RE:
HAMFESTS: ... \h symbol ... object name of HFEST-ddx where dd is the day of the month, and "x" is the next unused symbol. 

I believe I understand "\h symbol".  
HOWEVER...

Please explain "...next unused symbol...".  
Unused by whom, or where?
What is this symbol's universe (to choose from)? ASCII, APRS symbols...?

-- 
73, Steve, K9DCI