WebCore contains a set of ​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 ​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/JSClassNameCustom.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.