Gabriel Ivăncescu (@insn) commented about dlls/mshtml/mshtml_private_iface.idl:
HRESULT matchMedia([in] BSTR media_query, [retval, out] IDispatch **media_query_list); [id(54)] HRESULT postMessage([in] VARIANT msg, [in] BSTR targetOrigin, [in, optional] VARIANT transfer);
- [id(55)]
- HRESULT MutationObserver([in] IDispatch *callback, [retval, out] IDispatch **observer);
See comment above to turn it into a getter for the constructor (with named DISPID for the hook maybe).