Let's jump in to using some of the Layer class functions.
Open up the second WMS example, chapter3_ex2_options_config.html in Firefox. We won't be editing the code yet.
Enable Firebug and go to the Console panel.
In the console, input and run this line of code:
map.layers;
You should then see a list of layers.
You just accessed the layers property of the global map object. This is a property of the map object that contains an array of all the layers in the map. The list is ordered by the way you add layers to the map, so the first item in the list corresponds to the first layer we added to the map, the wms_layer_map layer. Not only will Firebug list the layer objects, you can also access any one of them by clicking on them.