Index: node.module
===================================================================
--- node.module	(revision 1146)
+++ node.module	(working copy)
@@ -2894,15 +2894,21 @@
   if (!$grants) {
     $grants[] = array('realm' => 'all', 'gid' => 0, 'grant_view' => 1, 'grant_update' => 0, 'grant_delete' => 0);
   }
-  else {
-    // retain grants by highest priority
-    $grant_by_priority = array();
-    foreach ($grants as $g) {
-      $grant_by_priority[intval($g['priority'])][] = $g;
-    }
-    krsort($grant_by_priority);
-    $grants = array_shift($grant_by_priority);
+
+  // Allow modules to customize node_access logic.  For example, to AND realms
+  // together rather than OR them.
+  foreach (module_implements('node_access_grants_alter') as $module) {
+    $function = $module .'_node_access_grants_alter';
+    $function($node, $grants);
   }
+  
+  // retain grants by highest priority
+  $grant_by_priority = array();
+  foreach ($grants as $g) {
+    $grant_by_priority[intval($g['priority'])][] = $g;
+  }
+  krsort($grant_by_priority);
+  $grants = array_shift($grant_by_priority);
 
   node_access_write_grants($node, $grants);
 }