Those domains that can support VLAN swapping will need to add a SwitchingService entry to their topology. After a discussion with Freek on the topic we have agreed on this example:

<nml:SwitchingService id="urn:ogf:network:example.net:2012:vidSwitchingService"
encoding="http://schemas.ogf.org/nml/2013/03/ethernet#ieee802.1q"
labelSwapping="true">
<nml:Relation type="http://schemas.ogf.org/nml/2013/03/base#hasInboundPort">
<nml:Port id="urn:ogf:network:example.net:2012:nodeA:port_X:1780:in"/>
<nml:Port id="urn:ogf:network:example.net:2012:nodeA:port_Y:1781:in"/>
</nml:Relation>
<nml:Relation type="http://schemas.ogf.org/nml/2013/03/base#hasOutboundPort">
<nml:Port id="urn:ogf:network:example.net:2012:nodeA:port_X:1780:out"/>
<nml:Port id="urn:ogf:network:example.net:2012:nodeA:port_Y:1781:out"/>
</nml:Relation>
</nml:SwitchingService>

This follows the standard NML pattern in that both Port and PortGroup are supported but not BiDirectionalPort. If you notice we have an issue with the ethernet namespace in that it has not been standardized, and depending on if you look at the NML standard or the A-GOLE topologies, we either using the http://schemas.ogf.org/nml/2013/05/ethernet or the http://schemas.ogf.org/nml/2012/10/ethernet namespace identifier. We need to create a formalized Ethernet document for reference and designate a namespace for our topologies. We can then capture and document the specific URI fragments (vlan, ieee802.1q, etc.). I will discuss this with Freek.