Merge pull request #281 from patcg-individual-drafts/akatcoff-top-top…

…ics-selection

Top topics selection with prioritization

README.md

@@ -133,12 +133,15 @@ The topics will be inferred by the browser. The browser will leverage a classifi
         * Please see below for discussion on allowing sites to set their own topics.
     * The mapping of hostnames to topics will be updated over time, but the cadence is TBD.
 * How the top five topics for the epoch are selected:
-    * At the end of an epoch, the browser calculates the list of eligible pages visited by the user in the previous week 
-        * Eligible visits are those that used the API, and the API wasn’t disabled
-            * e.g., disabled by preference or site response header
-    * For each page, the host portion of the URL is mapped to its list of topics
-    * The topics are accumulated
-    * The top five topics are chosen
+    * Topics are sorted by a two-level sort – first by priority level and then by visit count.
+    * Priority:
+        * Each root-level topic (e.g. /Arts & Entertainment or /Autos & Vehicles) in the taxonomy is assigned a binary priority level based on industry input. The root-level topic’s descendants inherit its priority. A topic’s priority is universal across all epoch calculations for all users.
+    * Visit count:
+        * At the end of an epoch, the browser calculates the list of eligible pages visited by the user in the previous week
+            * Eligible visits are those that used the API, and the API wasn’t disabled
+                * e.g., disabled by preference or site response header
+        * For each page, the host portion of the URL is mapped to its list of topics
+        * The topics are accumulated
 * If the user opts out of the Topics API, or is in incognito mode, or the user has cleared all of their history, the list of topics returned will be empty
     * We considered a random response instead of empty but prefer empty because:
         * It’s clearer to users to see that after disabling the feature, or entering incognito, that no topic is sent