'named sets' in BIND 931 masters clause not behaving ...

[OpenMacNews]

hi all,

i'm trying to use a 'named set' in a slave zones' 'masters' clause in BIND931 
on OSX 10.4.2.

from the bind 9.3.x release notes,

 "It is now possible to define a named set of master servers to be
  used in masters clause, masters."

i can't seem to find any add'l info/doc on these "named sets" ... reference?

assuming they're defined as acl's, if I define in named.conf:

    ...
    acl test_masters_set { 1.1.1.1; 2.2.2.2; };
    ...
    zone "mydomain.com" IN {
		type slave; file "mydomain.com.hosts";
		masters { test_masters_set; };
	};
    ...

then,

    % rndc reload
        rndc: 'reload' failed: failure

w/ bind-log showing:

    general: info: loading configuration from '.../named.conf'
    config: error: .../named.conf:199: unable to find masters list 
'test_masters_set'
    general: error: reloading configuration failed: failure


however, if i replace the set reference with a list of IP addr,

    zone "mydomain.com" IN {
		type slave; file "mydomain.com.hosts";
		masters { 1.1.1.1; 2.2.2.2; };
	};

then,

    % rndc reload
        server reload successful

and my transfer completes successfully ...

what am i missing?

thx,

richard