CategorySearch - why the query parameter?

I like the TomTom APIs. They are easy to use, the JSON responses are easy to understand and to parse and the speed is excellent. The one thing I find rather confusing is this - why does a category search require a query parameter. The URL for a category search bears the form

[type or paste code here](,7318006,7318008&view=Unified&relatedPois=off&key=*****)

I would like to be able to search for specified categories around a given lat/long pair with a specified radius. I would then parse and classify the results based on the reported category for each hit.

In the example above my three categories correspond to Theatre,Caberet Theatre and Dinner Theatre so Amphitheatre and Cinema Theatre don’t currupt the result set. However, as things stand this query will not work. To get it to work I will have to change the URL so QUERY = theatre

This does not seem terribly logical to me. Perhaps someone here would care to explain?

If the categorySet is used then there is no need to provide the query param.,7318006,7318008&view=Unified&relatedPois=off&key=*****