WebCore contains a set of [http://www.w3.org/TR/WebIDL/ IDL files] which define the public interface that WebCore classes expose to Javascript and ObjectiveC. These IDL files are parsed and code is automatically generated which maintains a "binding" between an external interface (e.g. a Javascript object) and the internal WebCore implementations. The format of these files are fairly well documented and (mostly) adhere to the syntax described in the [http://www.w3.org/TR/WebIDL/ w3c specification], but there are several differences which are noted below. The ''interface'' declaration takes an optional set of attributes: Conditional=''CONDITIONALNAME'':: Wraps the generated binding code in "#if ENABLE(''CONDITIONALNAME'')". Typically used to allow turning off features on certain platforms (or to disable new features while they are under development). CustomMarkFunction:: Adds a "virtual void mark()" declaration to the generated header file for the binding class. This allows a custom binding implementation to provide their own mark() function in WebCore/bindings/js/JS''ClassName''Custom.cpp for doing custom handling of garbage collection. DelegatingGetOwnPropertySlot:: Used when a given instance wants to customize the lookup of properties. Examples are the HTML History object, which needs to enforce restrictions on which attributes are visible cross-domain, or WorkerContext, which wants to delegate lookup to the global object before looking up properties in its own prototype. ExtendsDOMGlobalObject:: Does not expose the object prototype externally, as the class cannot be derived from externally. Also uses this object internally whenever it needs to access the JSDOMGlobalObject. LegacyParent=''ParentClass'':: Allows setting the base class for the generated binding. Otherwise, the base class would be set to DOMObject or the explicitly specified parent class in the interface definition.