Unless I'm missing something, this seems to be re-inventing something that Underscore already gives you on Backbone collections, _.each():

  var mycollection = new MyCollection();
  ...
  mycollection.each(function(model) {
    model.set({'passesFilterXYZ': filterXYZ(model)});
  });

EDIT: it also makes an entirely new collection instance representing the set of filtered models...this seems terribly inefficient compared to the above.

I was hoping he had implemented filtering and paging by fetching and caching the required objects from the server (overloading Backbone.Collection.fetch or Backbone.Sync). Instead this is just slicing the arrays different ways; to paginate/filter with it you still fetch 1000 models and only show 10 at a time, or whatever option you pass.

See: http://en.wikipedia.org/wiki/Chain-of-responsibility_pattern

Maybe I am citing the wrong pattern here. Basically each collection "filter" will do it's own work and pretend like it in itselfis a collection. The pagination is like a collection, but filtered in some way, the filtering is too. Eventually I can easily implement another in the chain to fetch records when I page to the page containing the record (say the record really only contains the ID) and it would be pretty trivial to do.

Also lets you have a master collection of data, and multiple views doing different things with that master collection, without constantly changing the master.