code: function(options) {
          options = OpenLayers.Util.extend({
              featurePrefix: this.featurePrefix,
              schema: this.schema
          }, options);
          var schemaLocations = OpenLayers.Util.extend({}, this.schemaLocations);
          if(options.schema) {
              schemaLocations[options.featurePrefix] = options.schema;
          }
          var parts = [];
          var uri;
          for(var key in schemaLocations) {
              uri = this.namespaces[key];
              if(uri) {
                  parts.push(uri + " " + schemaLocations[key]);
              }
          }
          var value = parts.join(" ") || undefined;
          return value;
      }
docs: Method: schemaLocationAttr
  Generate the xsi:schemaLocation attribute value.
  
  Returns:
  {String} The xsi:schemaLocation attribute or undefined if none.