TodosModel

gistfile1.js

maria.SetModel.subclass(checkit, 'TodosModel', {
    methods: {
        getDone: function() {
            return this.filter(function(todo) {
                return todo.isDone();
            });
        },
        getUndone: function() {
            return this.filter(function(todo) {
                return !todo.isDone();
            });
        },
        markAllDone: function() {
            this.forEach(function(todo) {
                todo.setDone(true);
            });
        },
        markAllUndone: function() {
            this.forEach(function(todo) {
                todo.setDone(false);
            });
        },
        deleteDone: function() {
            this['delete'].apply(this, this.getDone());
        }
    }
});

// ----
//
// var todos = new checkit.TodosModel(); // create a todos set
// todos.add(new checkit.TodoModel());   // add a todo to the set

What's the rational for subclass to create a global variable rather then for it to return the new class ?

It doesn't create a global. It adds a constructor function to the provided namespace object which, in this case, is the checkit object.

My mistake, why does it strip the "Model" of the name of the constructor?

That was a mistake in the commented code at the bottom. Fixed now.