handling of 'sensor_type' attribute of 'sensor resource' is vague

The section that describes the 'sensor_type' attribute of the 'sensor resource' (section 5.26.3 in WD 04) reads:
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This attribute specifies the type of the data that this sensor resource collects. For example, "String", "Timestamp". Attribute types are defined in Section 5.2, “Attribute Types”. type_definitions may also be used to specify types. See Section 5.18, “type_definitions Resource”.
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When we say 'type_definitions may also be used' it's not clear what Consumers should expect the value of this attribute to be. One could guess that the value is supposed to be the name of the type, but that would only be a guess. An equally valid guess might be the URI of the 'type_definition resource' that defines the type of the sensor. In any case there is an interoperability problem here in that independent implementations might make different, but equally valid, guesses.