From IAccessible to IHTMLElement and back

When developing Internet Explorer plug-ins you might want to take advantage of the dual nature of the browser objects. Internet Explorer exposes the DOM (document object model) using IHTMLElement interface as the building block of the hierarchy. It also offers accessible objects through Active Accessibility IAccessible interface.

// From IAccessible to IHTMLElement.
CComQIPtr<IHTMLElement> AccessibleToHTMLElement(IAccessible* pAccessible)
{
     ATLASSERT(pAccessible != NULL);

     // Query for IServiceProvider interface.
     CComQIPtr<IServiceProvider> spServProvider = pAccessible;
     if (spServProvider != NULL)
     {
         // Ask the service for a IHTMLElement object.
         CComQIPtr<IHTMLElement> spHtmlElement;
         HRESULT hRes = spServProvider->QueryService(IID_IHTMLElement, IID_IHTMLElement,
                                                      (void**)&spHtmlElement);

         return spHtmlElement;
     }

     return CComQIPtr<IHTMLElement>();
}

// From IHTMLElement to IAccessible.
CComQIPtr<IAccessible> HTMLElementToAccessible(IHTMLElement* pHtmlElement)
{
     ATLASSERT(pHtmlElement != NULL);

     // Query for IServiceProvider interface.
     CComQIPtr<IServiceProvider> spServProvider = pHtmlElement;
     if (spServProvider != NULL)
     {
         // Ask the service for a IAccessible object.
         CComQIPtr<IAccessible> spAccessible;
         HRESULT hRes = spServProvider->QueryService(IID_IAccessible, IID_IAccessible,
                                                      (void**)&spAccessible);

         return spAccessible;
     }

     return CComQIPtr<IAccessible>();
}

Not all IHTMLElement objects support Active Accessibility. Here is the list of the HTML elements that are also accessible elements:
A, AREA, BUTTON, INPUT type=BUTTON, INPUT type=RESET, INPUT type=SUBMIT, FRAME, IMG, INPUT type=checkbox, INPUT type=image, INPUT type=password, INPUT type=radio, MARQUEE, OBJECT, APPLET, EMBED, SELECT, TABLE, TD, TH, TEXTAREA, INPUT type=TEXT.

This technique was successfully implemented and tested in My web automation library.
codeproject