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.

  CustomToJS::
  Does not generate a toJS() function for the binding class. This allows implementors to provide their own toJS() function to create the correct wrapper class for a given implementation class. This is useful whenever you have a class hierarchy in the implementing classes - when given an instance of the base class, the custom toJS() implementation should return a wrapper appropriate to the derived class, not the base class.

  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. Also uses a self-reference internally whenever it needs to access the JSDOMGlobalObject.

  GenerateConstructor::
  Generates code to enable the class to be externally instantiated.

  GenerateNativeConverter::
  Generates a helper function of the form ''ClassName''* impl() { return static_cast<''ClassName''>(m_impl); }. Useful when working with a class hierarchy in the binding code, where the base m_impl member is defined to be the base type, not the appropriate derived type.

  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.

  NoStaticTables::
 Sharing a single static prototype table only works when a class is guaranteed to be accessed from a single heap, because the lookup code expects the key (attribute name) to have the same address across all instances of the object. For interfaces that are exposed to Workers, a single static table won't work because a given string used to look up a property on the object will lie at a different address in each heap.

See [http://trac.webkit.org/wiki/WebKitIDL WebKitIDL] for detailed documentation.