CouchDB sorting and filtering in the same view

I'm trying to use CouchDB for a new app, and I need to create a view that sorts by multiple fields and also filters by multiple fields. Here is an example document, I've left out the _id and _rev to save myself some typing.

{
    "title": "My Document",
    "date": 1279816057,
    "ranking": 5,
    "category": "fun",
    "tags": [
        "couchdb",
        "technology"
    ],
}

From the documentation, I've learned that I can easily create a view that sorts by a field such as ranking.

function(doc) {
    emit(doc.ranking, doc);
}

I've also learned that I can easily filter by fields such as category

function(doc) {
    emit(doc.category, doc);
}

http://127.0.0.1:5984/database/_design/filter/_view/filter?key=%22fun%22

My problem is that I need to do a bunch of these things all at the same time. I want to filter based on category and also tag. I should be able to filter down to only documents with category of "fun" and tag of "couchdb". I want to sort those filtered results by ranking in descending order, then by date in ascending order, then by title in alphabetical order.

How can I create one view that does all of that sorting and filtering combined?