code: function(e) {
      var target = e.target || e.srcElement;
      if (e.keyCode === 8) {
        if (target.getAttribute('contenteditable') ||
            target.tagName === 'INPUT' ||
            target.tagName === 'TEXTAREA') {
          return;
        }
  
        e.preventDefault();
      }
    }
docs: /*
  Disable back button so when a block loses focus the user
  pressing backspace multiple times doesn't close the page.