diff --git a/modules/mtree/doc/mtree_admin.xml b/modules/mtree/doc/mtree_admin.xml
index 17c2c8fbacb..8ca17e006c2 100644
--- a/modules/mtree/doc/mtree_admin.xml
+++ b/modules/mtree/doc/mtree_admin.xml
@@ -17,8 +17,18 @@
Overview
- This module loads data indexed by prefixes from database and returns
- associated string or precompiled value.
+ This module loads (prefix, value) records from database and indexes
+ them in a named memory tree. Name of the tree is specified for each
+ record or as module parameter.
+
+
+ It exports to configuration file functions to match against in-memory
+ trees and return the values (raw or precompiled) associated with
+ matched prefixes.
+
+
+ The maximum size of the prefix is limited internally to 63, database
+ table definition may enforce lower maximum size.