Can someone explain this clause in the default AA OutboundCallRoute?

[plugger2]

The first clause in the default AA OutboundCallRoute is:

{([1-9]x?*(Mpli)):pp}

Can someone explain exactly what the left side matches (in particular, what is the meaning of the "?" in this context?)

The target port id the p2p (ObiTalk) port, so I assume this is to capture and direct p2p requests of some description. Why the primary line digitmap Mpli used for this?
 

[obi-support2]

This rule is added by default in 1.2 f/w to support ad hoc 1-stage gateway calls (using OBiTALK trunk only at the moment). You can configure the obi number of another OBi (gateway) in a speed dial (1-99). To call out using that gateway, dial <speed-dial> * <target-number>. Since  AuthUserID/AuthPassword are not specifiable in a speed dial, this method only works if the gateway does not require HTTP Digest authentication.

x? means 0 or 1 x, so [1-9]x? maps to 1-99, a speed dial.