docs: function(id, querydef) {
          // find the matching layer, if it exists
          for (var lyr = 0; lyr < this.options.layers.length; lyr++) {
              if (id == this.options.layers[lyr].id) {
                  // replace this layer definition
                  this.options.layers[lyr].query = querydef;
                  return;
              }
          }
        
          // no layer found, create a new definition
          this.options.layers.push({id: id, visible: true, query: querydef});
      }