class EventTarget : public nsISupports, public nsWrapperCache { ... };

// File: dom/base/nsINode.h
// The core DOM Node interface; defines child/parent navigation, nodeType, etc.
class nsINode { ... };

// File: dom/base/FragmentOrElement.h
// Container node for Element and DocumentFragment (implements nsINode + nsIContent).
class FragmentOrElement : public nsINode, public nsIContent { ... };

// File: dom/base/Element.h
// Base class for all element nodes (provides attribute handling, styling hooks, etc.).
class Element : public FragmentOrElement { ... };

// File: dom/html/HTMLElement.h
// HTML-specific element base (inherits from nsGenericHTMLElement).
class HTMLElement : public nsGenericHTMLElement { ... };

// File: dom/base/Document.h
// The root of the DOM tree; also implements document-level methods and lifecycle.
class Document : public FragmentOrElement, /* ...other interfaces... */{ ... };

// File: dom/base/CharacterData.h
// Base for all character-data nodes: Comment, Text, CDATASection, etc.
class CharacterData : public nsINode { ... };

// File: dom/base/CharacterData.cpp
// The Text class, representing text nodes in the DOM.
class Text : public CharacterData { ... };