code: function convertElement (el, self) {
    if (el instanceof Schema) {
      return el.toObject(self);
    }
  
    if (isObject(el)) {
      return convertObject(el, self);
    }
  
    if (Array.isArray(el)) {
      return el.map(function (item) {
        return convertElement(item, self);
      })
    }
  
    return el;
  }
docs: Converts a single element to plain object