A subscription contains the following information:
Publisher. For example, M3
Document name. For example, OOHEAD
One or several event operations
A subscription also provides properties for guaranteed event sequence (not implemented yet) and event priority (P1, P2, and P3).
A subscription can be defined by a single string using the following layout (BNF format):
<syntax> ::= <publisher> ":" <documentName> [":" [<operation char>] [":" [("true" | "false")] [":"[<priority>]]]]
For example, M3:OOHEAD:CUD:false:P2
A subscriber needs to define at least one subscription to receive any events.