When this message is produced by a device instead of the controller, it signals that the prim <key> can provide port functionality of the type <type>. This means that it should be used as a particle target for wires emitted by base stations. Port types supported by Nanoconnectivity 1.6:

class
power
audio-in
audio-out
data-1
data-2

Note that if the controller sends this message, it instead indicates a redirect to another device; see port-real and the entries above it.