- optionally `!' or `+' followed by a glob pattern (which is applied to a
- prospective interface using fnmatch with no flags). If no list is
- specified, or the list ends with a `!' entry, a default list is
- used/appended: "!tun*","!tap*","!sl*","!userv*","!lo","*". Patterns
- which do not start with `*' or an alphanumeric need to be preceded
- by `!' or `+'.
+ optionally `!' or `+' or `@' followed by a glob pattern (which is
+ applied to a prospective interface using fnmatch with no flags).
+ `+' or nothing means to process normally. `!' means to ignore;
+ `@' means to use only in conjunction with dedicated-interface-addr.
+ If no list is specified, or the list ends with a `!' entry, a
+ default list is used/appended:
+ "!tun*","!tap*","!sl*","!userv*","!lo","@hippo*","*".
+ Patterns which do not start with `*' or an alphanumeric need to be
+ preceded by `!' or `+' or `@'.