In the current TOSCA schema and spec, all definitions go into a <ServiceTemplate> root element. This can be confusing, e.g. if someone has to define a <ServiceTemplate> when just wanting to provide a new NodeType. <ServiceTemplate> should really just be the service template, and all other definitions should go into a different root. The rough structure would be like:

<ServiceTemplate>
...
<TopologyTemplate>
...
</TopologyTemplate>

<Plans>
...
</Plans>
</ServiceTemplate>

and then a separate root element for definitions

<Definitions>
...
(
<NodeType>
...
</NodeType>

<RelationshipType>
...
</RelationshipType>

...
)+

</Definitions>

I will prepare a version of the spec and schema based on the next complete WD according to the outline above.