code: function(features, options) {
          var node = this.writeNode("wfs:Transaction", {
              features:features,
              options: options
          });
          var value = this.schemaLocationAttr();
          if(value) {
              this.setAttributeNS(
                  node, this.namespaces["xsi"], "xsi:schemaLocation",  value
              );
          }
          return OpenLayers.Format.XML.prototype.write.apply(this, [node]);
      }
docs: Method: write
  Given an array of features, write a WFS transaction.  This assumes
  the features have a state property that determines the operation
  type - insert, update, or delete.
  
  Parameters:
  features - {Array(<OpenLayers.Feature.Vector>)} A list of features. See
  below for a more detailed description of the influence of the
  feature's *modified* property.
  options - {Object}
  
  feature.modified rules:
  If a feature has a modified property set, the following checks will be
  made before a feature's geometry or attribute is included in an Update
  transaction:
  - *modified* is not set at all: The geometry and all attributes will be
  included.
  - *modified.geometry* is set (null or a geometry): The geometry will be
  included. If *modified.attributes* is not set, all attributes will
  be included.
  - *modified.attributes* is set: Only the attributes set (i.e. to null or
  a value) in *modified.attributes* will be included.
  If *modified.geometry* is not set, the geometry will not be included.
  
  Valid options include:
  - *multi* {Boolean} If set to true, geometries will be casted to
  Multi geometries before writing.
  
  Returns:
  {String} A serialized WFS transaction.