Modules installed in dnn have the ability to subscribe themselves to the dnn search crawler. By doing this the contents of a module can be indexed.

As to what exactly is indexed - well that depends on the module - but in most cases modules pass in the relevant content from the module. This does get complicated however with modules such as shopping carts or repositories that need to make sometimes complicated decisions about how they interact with the search engine. Remember that many modules can serve up many different pages of content depending on the user context.

As such however, there is little or no metadata or context relative information stored in the core index. Effectively - whatever content is passed into the search crawler from each module is simply indexed at the word level.

As to how you could create category based searches - yes you could in theory create a modified search tool - that worked with the core index data.

Westa