[exim] Route_data format

I have been using a route_data statement in a manualroute router for
quite some time as:

route_data = mr01.ex.ac.uk:rr01.ex.ac.uk

That routes everything via the first server, with the second as backup.

I want to add a second server alongside the first, with hosts_randomize
set true. Can I use:

route_data = mr01.ex.ac.uk:mr02.ex.ac.uk:+:rr01.ex.ac.uk

The use of ':+:' to separate groups of addresses is described in the
spec for hosts_randomize with a route_list example. It is not clear if
the same syntax will work for route_data.

Can anyone clarify this for me please?

Phil.
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Phil Chambers
Postmaster
University of Exeter