Add brief platform documentation for UI Automation

This is a short document targeted at engineers working on accessibility
who aren't familiar with UIA. The intent is to identify the most
important points to consider when looking at UIA-specific test results
and to provide links to deeper documentation on MSDN.

This CL also fixes up incorrectly marked-up links I noticed on the
Android accessibility documentation page.

Bug: None
Change-Id: Iccfaf19eeae1659384244ac3f0a27e4596422c1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2957347
Reviewed-by: Daniel Libby <dlibby@microsoft.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Kevin Babbitt <kbabbitt@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#892172}

docs/accessibility/android.md

@@ -8,16 +8,16 @@ This document covers some of the technical details of how Chrome
 implements its accessibility support on Android.
 
 As background reading, you should be familiar with
-[https://developer.android.com/guide/topics/ui/accessibility](Android Accessibility)
+[Android Accessibility](https://developer.android.com/guide/topics/ui/accessibility)
 and in particular
-[https://developer.android.com/reference/android/view/accessibility/AccessibilityNodeInfo](AccessibilityNodeInfo)
+[AccessibilityNodeInfo](https://developer.android.com/reference/android/view/accessibility/AccessibilityNodeInfo)
 and
-[https://developer.android.com/reference/android/view/accessibility/AccessibilityNodeProvider](AccessibilityNodeProvider).
+[AccessibilityNodeProvider](https://developer.android.com/reference/android/view/accessibility/AccessibilityNodeProvider).
 
 ## WebContentsAccessibility
 
 The main Java class that implements the accessibility protocol in Chrome is
-[https://cs.chromium.org/chromium/src/content/public/android/java/src/org/chromium/content/browser/accessibility/WebContentsAccessibilityImpl.java](WebContentsAccessibilityImpl.java). It implements the AccessibilityNodeProvider
+[WebContentsAccessibilityImpl.java](https://cs.chromium.org/chromium/src/content/public/android/java/src/org/chromium/content/browser/accessibility/WebContentsAccessibilityImpl.java). It implements the AccessibilityNodeProvider
 interface, so a single Android View can be represented by an entire tree
 of virtual views. Note that WebContentsAccessibilityImpl represents an
 entire web page, including all frames. The ids in the java code are unique IDs,
@@ -44,7 +44,7 @@ point. That's called by the Android framework when we need to provide the
 info about one virtual view (a web node).
 
 We call into C++ code - 
-[https://cs.chromium.org/chromium/src/content/browser/accessibility/web_contents_accessibility_android.cc](web_contents_accessibility_android.cc) from
+[web_contents_accessibility_android.cc](https://cs.chromium.org/chromium/src/content/browser/accessibility/web_contents_accessibility_android.cc) from
 there, because all of the information about the accessibility tree is
 using the shared C++ BrowserAccessibilityManager code.
 

docs/accessibility/overview.md

@@ -215,6 +215,14 @@ Automation Inspector Chrome extension).
   - macOS: Accessibility Inspector
   - Windows: Inspect, AViewer, accProbe (and many others)
 
+### Supported Platforms and APIs
+
+* Windows: IAccessible (also known as Microsoft Active Accessibility or MSAA),
+  IAccessible2, [UI Automation](uiautomation.md). Chromium also supports
+  [mapping between IAccessible2 and UI Automation nodes](ia2_to_uia.md).
+* Mac: NSAccessibility
+* Linux: ATK
+* Android: [AccessibilityNodeInfo and AccessibilityNodeProvider](android.md)
 
 ## Chromium's multi-process architecture
 

docs/accessibility/uiautomation.md

@@ -0,0 +1,53 @@
+# UI Automation
+
+[UI Automation (UIA)](https://docs.microsoft.com/en-us/windows/win32/winauto/entry-uiauto-win32)
+is the modern accessibility API on Windows.
+
+## Key Features
+
+### Clients and Providers
+
+UI Automation exposes two different sets of interfaces. One is intended for
+clients such as assistive technologies and automation frameworks. The other is
+intended for providers such as UI widget frameworks and applications that render
+their own content. Chromium implements the UI Automation provider APIs.
+
+Clients and providers do not talk directly to one another. Instead, the
+operating system gathers data from providers to present a unified tree view
+across all open applications to the client.
+
+Further reading:
+
+* [UI Automation Provider Programmer's Guide](https://docs.microsoft.com/en-us/windows/win32/winauto/uiauto-providerportal)
+* [UI Automation Client Programmer's Guide](https://docs.microsoft.com/en-us/windows/win32/winauto/uiauto-clientportal)
+
+### Views of the UI Automation tree
+
+Clients have the ability to filter the UI Automation tree to various subsets of
+nodes. Tools such as Windows Narrator take advantage of this capability to skip
+over structural details that might be interesting to an automation framework but
+aren't relevant to a screen reader.
+
+Providers can set two properties on a node to determine which views it appears
+in: IsControlElement and IsContentElement. Getting the value of these properties
+right is critical to ensuring assistive technologies can get the information
+they need. Despite the names, there are many cases where nodes that might not be
+considered a "control" should appear in the Control view of the tree. A good
+litmus test is: if there's a reason a screen reader might be interested in a
+node, it should appear in the control view.
+
+Further reading:
+
+* [UI Automation Tree Overview](https://docs.microsoft.com/en-us/windows/win32/winauto/uiauto-treeoverview)
+
+### TextPattern
+
+In addition to the tree view, UI Automation exposes a linear reading view
+through an API known as TextPattern. This API allows a screen reader to navigate
+text in more natural ways - characters, words, sentences, paragraphs, pages -
+without worrying about the underlying tree structure. Windows Narrator relies
+heavily on TextPattern for reading.
+
+Further reading:
+
+* [Text and TextRange Control Patterns](https://docs.microsoft.com/en-us/windows/win32/winauto/uiauto-implementingtextandtextrange)