So far, we've only been using the OpenLayers.Layer.WMS class in the examples. This has been the beginning of all our layer object instantiation code so far:
var wms = new OpenLayers.Layer.WMS(
Notice the period between Layer and WMS: Layer.WMS. This means that we're accessing the WMS subclass of the Layer superclass. What do I mean when I say this? Well, the WMS class is a subclass of the Layer class, so let's briefly refresh our knowledge about subclasses.
In Chapter 1, we mentioned Subclasses. Subclasses are, basically, classes that derive from some base class. This base class is called a Superclass. The Layer class is thus the Superclass of all Layer subclasses (Superclasses and Subclasses are still classes). Subclasses inherit all the properties of their superclass.