diff --git a/modules/node/node.module b/modules/node/node.module
index 516595a55ca7592dc181396be50cb454ae2bf65b..e6051e65c85631fd7d80bcf7f918e7e41613b9b3 100644
--- a/modules/node/node.module
+++ b/modules/node/node.module
@@ -7,6 +7,12 @@
  * programmatically submit nodes using the usual form API pattern.
  */
 
+/**
+ * Nodes changed before this time are always marked as read.
+ *
+ * Nodes changed after this time may be marked new, updated, or read, depending
+ * on their state for the current user. Defaults to 30 days ago.
+ */
 define('NODE_NEW_LIMIT', time() - 30 * 24 * 60 * 60);
 
 define('NODE_BUILD_NORMAL', 0);