Expands javadocs for Intent.FLAG_ACTIVITY_MATCH_EXTERNAL

This change adds much needed detail to the new MATCH_EXTERNAL flag,
explaining some of the behavior changes that come with using it.

Test: none
Bug: 63117034
Bug: 79325769
Change-Id: Iab320d2171ffe8d8012a2928656ea61d5e0f0862
diff --git a/core/java/android/content/Intent.java b/core/java/android/content/Intent.java
index dec2cd4..fe48975 100644
--- a/core/java/android/content/Intent.java
+++ b/core/java/android/content/Intent.java
@@ -5683,9 +5683,24 @@
 
 
     /**
-     * If set, resolution of this intent may take place via an instant app not
-     * yet on the device if there does not yet exist an app on device to
-     * resolve it.
+     * If set in an Intent passed to {@link Context#startActivity Context.startActivity()},
+     * this flag will attempt to launch an instant app if no full app on the device can already
+     * handle the intent.
+     * <p>
+     * When attempting to resolve instant apps externally, the following {@link Intent} properties
+     * are supported:
+     * <ul>
+     *     <li>{@link Intent#setAction(String)}</li>
+     *     <li>{@link Intent#addCategory(String)}</li>
+     *     <li>{@link Intent#setData(Uri)}</li>
+     *     <li>{@link Intent#setType(String)}</li>
+     *     <li>{@link Intent#setPackage(String)}</li>
+     *     <li>{@link Intent#addFlags(int)}</li>
+     * </ul>
+     * <p>
+     * In the case that no instant app can be found, the installer will be launched to notify the
+     * user that the intent could not be resolved. On devices that do not support instant apps,
+     * the flag will be ignored.
      */
     public static final int FLAG_ACTIVITY_MATCH_EXTERNAL = 0x00000800;