Create AutomationProvider.md

Author: bradp0721

specs/AutomationProvider.md

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+# Background
+WebView has two hosting modes, windowed (which uses the ICoreWebView2Controller) and visual (which uses the ICoreWebView2CompositionController). Accessibility for the windowed WebView is able to walk the HWND tree to know where to place the WebView in the accessibility tree. For visual hosting, accessibility is not able to know where within the accessibility tree to place the WebView. This results in a WebView being a sibling to the rest of the app content.
+
+In this document we describe the updated API. We'd appreciate your feedback.
+
+
+# Description
+To give apps using the ICoreWebView2CompositionController more control over how the WebView is positioned in the accessibility tree, we are adding new APIs to let the app retrieve the automation provider for the WebView. This let's the app return the automation provider as part of its accessibility tree.
+
+While traversing child elements, when the app reaches the WebView, it can use the `UIAProvider` property to get the automation provider for the WebView and return it.
+
+When accessibility is traversing parent elements, the app can use `GetProviderForHwnd` to get the automation provider that matches the WebView based on the HWND.
+
+# Examples
+```cpp
+HRESULT WebView2AutomationPeer::GetRawElementProviderSimple(IRawElementProviderSimple** value)
+{
+    wil::com_ptr<IUnknown> provider;
+    CHECK_FAILURE(m_controller->get_UIAProvider(&provider));
+    return provider->QueryInterface(IID_PPV_ARGS(value));
+}
+
+bool WebView2AutomationPeer::IsCorrectPeerForHwnd(HWND hwnd)
+{
+    wil::com_ptr<IUnknown> provider;
+    CHECK_FAILURE(m_controller->get_UIAProvider(&provider));
+
+    wil::com_ptr<IUnknown> providerForHwnd;
+    CHECK_FAILURE(m_environment->GetProviderForHwnd(hwnd, &providerForHwnd));
+
+    return (provider == providerForHwnd);
+}
+```
+
+# API Notes
+See [API Details](#api_details) section below for API reference.
+
+# API Details
+## Win32 C++
+``` c#
+interface ICoreWebView2Environment4 : ICoreWebView2Environment3 {
+  /// Returns the UI Automation Provider for the
+  /// ICoreWebView2CompositionController that corresponds with the given HWND.
+  HRESULT GetProviderForHwnd([in] HWND hwnd,
+                             [out, retval] IUnknown** provider);
+}
+
+interface ICoreWebView2CompositionController2 : ICoreWebView2CompositionController {
+  /// Returns the UI Automation Provider for the WebView.
+  [propget] HRESULT UIAProvider([out, retval] IUnknown** provider);
+}
+```
+## .Net and WinRT
+API is not natively supported in .Net and WinRT. The Win32 COM API is exposed using an interop interface.