Edit in JSFiddle

var MyView = Backbone.View.extend({
    initialize:function(){
        this.render()
    },
    render:function(){
        //this.$() is shortcut for jQuery(this.el).find('span');
        //doing $('span') would find all span elements
        //using this.$('span') only finds/select span's in the el node
        this.$('span').css('font-weight','bold'); 
    }
});

var myViewInstance = new MyView({el:'#myView'});

<div id="myView"><span>Bold</span> not bold!</div>

<span>Bold</span> not bold!