code: function Duration(value, parameters) {
      abstractions.Element.call(this, utilities.types.DURATION, parameters);
      value = value || 0;  // the default value
      value = moment.duration(value);
  
      // since this element is immutable the value must be read-only
      this.getValue = function() { return value; };
  
      return this;
  }
docs: PUBLIC CONSTRUCTOR 
  This constructor creates a new duration element using the specified value.
  
  @param {String|Number} value The source string the duration.
  @param {Parameters} parameters Optional parameters used to parameterize this element.
  @returns {Duration} The new duration element.