diff --git a/changes.proto b/changes.proto
index 0b6603a..1085e79 100644
--- a/changes.proto
+++ b/changes.proto
@@ -272,6 +272,9 @@ message ListHomeChangesRequest {
   optional ChangeFiltersRequest filters = 2;
 }
 
+// ChangeFiltersRequest is used for filtering on the changes page.
+// Repeated entries of the same type are used to represent OR conditions. eg if repo is ["a", "b"] then the filter is (repo == "a" OR repo == "b")
+// The filters are ANDed together. eg if repo is ["a", "b"] and author is ["c"] then the filter is (repo == "a" OR repo == "b") AND author == "c"
 message ChangeFiltersRequest {
   repeated string repos = 1;
   map<string, string> tags = 2;