When we integrated GoodRelations, we skipped the category property for reasons I do not remember.

This should be fixed - simply add
<span>Domain: <a property="http://schema.org/domainIncludes" href="http://schema.org/Product">Product</a></span>

in the block for

<div typeof="rdf:Property" resource="http://schema.org/category">

This will also make this consistent with

http://www.heppnetz.de/ontologies/goodrelations/v1.html#category

@mfhepp FYI some of your markup didn't make it through the markdown parser. use triple backtick ```

Thanks, fixed.

I fixed the title, because it was about the domain, not the range of the property.

see also #160