Can you define instance method for sub documents in Mongoose?

If I have a a Schema in Mongoose that's defined like:

var subSchema = new Schema({
  some: String
});

var topSchema = new Schema({
  subs: [subSchema]
});

var topModel = mongoose.model("Top", topSchema);

Is it possible to define an instance method for the sub document? I've tried the following(added before the model declaration), but it doesn't work:

subSchema.methods.someFn = function() { 
  return 'blah';
};

Answering my own question.

What I originally wanted to do was to create a function that can be used on the collection of subdocs, as in:

topdoc.subs.someFn();

However, what I actually did with code in the original question was create a function for a subdoc itself, as in:

topdoc.subs[i].someFn();

This works.

As far as I can tell, creating a function for the collection of subdocs is not supported by Mongoose.

I got around this by defining a method in topSchema that would do what I want.