code: function addProperty(name, value) {
    if (typeof name !== 'string' || value == null) {
      throw new Error('properties.add() takes a string name and a value');
    }
    var prop = {};
    prop[name] = value;
    return insert('/object-node("properties")', 'last-child', prop);
  }
docs: Specifies operations to patch the metadata properties of a document.
  @namespace patchBuilderProperties
   
  Specifies a new property to add to a document's metadata.
  @method patchBuilderProperties#add
  @since 1.0
  @param {string} name - the name of the new metadata property
  @param value - the value of the new metadata property
  @returns {patchBuilder.PatchOperation} a patch operation