code: function el (d, data) {
    if (typeof d === 'object') return assign({}, d, data)
    else return assign({ duration: +d || 0 }, data)
  }
docs: Create a score element: an object with duration
  
  It's accepts any data you supply, but duration property has a special
  meaning: it's a number representing the duration in arbitrary units.
  It's assumed to be 0 (no duration) if not present or not a valid number
  
  @param {Number} duration - the element duration
  @param {Object} data - the additional element data