A string describing a complete, or partial 'Autonomyous System'
inwhich to perform matches.
This string uses a limited form of regular expression syntax
to define what values of an AS path to match. The special
characters used are '^' and '$' to specify 'start' and
'end' respectively.
100 - a path with 100 in it
^100$ - exactly the path of 100 (adjacent AS)
^100 - any path starting with 100
100$ - any path ending with 100
100.200 - a path with the sequence 100.200 in it.
note: this is only valid for routes sourced from BGP.