smartmontools how to specify platform 10.6, 10.7, 10.8

[Chris Murphy]

I've had smartmontools 5.4x working on 10.6 and 10.7 simply using:

port pkg smartmontools

Now, with smartmontools 6 this command produces an installation package that only works on 10.8. Maybe it's an Xcode thing I have no idea. But how do I specify platform?

Section 5.5.3 Platform Variants, the examples are totally non-obvious where they're supposed to go in the Portfile or how they are to be specified. When I merely insert:
platform darwin 10
platform darwin 11
platform darwin 12

I get:
Error: Unable to open port: invalid command name "10"

So what I'd really like is a single smartmontools 6 pkg that will install on intel 10.6, 10.7, and 10.8 systems. If I can't have that, I'd take
a.) universal (i386/x86_64) for 10.6 pkg
b.) x86_64 only for 10.7 and 10.8 pkg

Thanks,

Chris Murphy