Defaults and Alternates
-----------------------

   The first set of commands in the file, up to the first `system'
command, specify defaults to be used for all systems in that file.  Each
`sys' file uses a different set of defaults.

   Subsequently, each set of commands from `system' up to the next
`system' command describe a particular system.  Default values may be
overridden for specific systems.

   Each system may then have a series of alternate choices to use when
calling out or calling in.  The first set of commands for a particular
system, up to the first `alternate' command, provide the first choice.
Subsequently, each set of commands from `alternate' up to the next
`alternate' command describe an alternate choice for calling out or
calling in.

   When a system is called, the commands before the first `alternate'
are used to select a phone number, port, and so forth; if the call fails
for some reason, the commands between the first `alternate' and the
second are used, and so forth.  Well, not quite.  Actually, each
succeeding alternate will only be used if it is different in some
relevant way (different phone number, different chat script, etc.).  If
you want to force the same alternate to be used again (to retry a phone
call more than once, for example), enter the phone number (or any other
relevant field) again to make it appear different.

   The alternates can also be used to give different permissions to an
incoming call based on the login name.  This will only be done if the
first set of commands, before the first `alternate' command, uses the
`called-login' command.  The list of alternates will be searched, and
the first alternate with a matching `called-login' command will be
used.  If no alternates match, the call will be rejected.

   The `alternate' command may also be used in the file-wide defaults
(the set of commands before the first `system' command).  This might be
used to specify a list of ports which are available for all systems
(for an example of this, see See Gateway Example) or to specify
permissions based on the login name used by the remote system when it
calls in.  The first alternate for each system will default to the
first alternate for the file-wide defaults (as modified by the commands
used before the first `alternate' command for this system), the second
alternate for each system to the second alternate for the file-wide
defaults (as modified the same way), and so forth.  If a system
specifies more alternates than the file-wide defaults, the trailing
ones will default to the last file-wide default alternate.  If a system
specifies fewer alternates than the file-wide defaults, the trailing
file-wide default alternates will be used unmodified.  The
`default-alternates' command may be used to modify this behaviour.

   This can all get rather confusing, although it's easier to use than
to describe concisely; the `uuchk' program may be used to ensure that
you are getting what you want.