code: function() {
        var t = this,
            branches = t.model.get('branches'),
            leaves = t.model.get('leaves'),
            hash = "";
  
        // The hash is the text of the branches & leaves
        branches && branches.forEach(function(node) {
          var label = node.get('label') || node.id,
              description = node.get('description');
          hash += '|' + label;
          if (description) {
            hash += '|' + description;
          }
        });
  
        // The hash is the text of the branches & leaves
        leaves && leaves.forEach(function(node) {
          var label = node.get('label') || node.id,
              description = node.get('description');
          hash += '|' + label;
          if (description) {
            hash += '|' + description;
          }
        });
  
        // Return the hash
        return hash;
      }
docs: Return a hash code representing the visual state of the underlying data model.  This is compared with subsequent states to prevent too much re-rendering.