diff --git a/libisofs/builder.c b/libisofs/builder.c
index 26c53d5..ef509ce 100644
--- a/libisofs/builder.c
+++ b/libisofs/builder.c
@@ -246,6 +246,9 @@ int default_create_node(IsoNodeBuilder *builder, IsoImage *image,
 static
 void default_free(IsoNodeBuilder *builder)
 {
+    /* The .free() method of IsoNodeBuilder shall free private data but not
+       the builder itself. The latter is done in iso_node_builder_unref().
+    */
     return;
 }
 
diff --git a/libisofs/libisofs.h b/libisofs/libisofs.h
index dc3d9e6..a98271d 100644
--- a/libisofs/libisofs.h
+++ b/libisofs/libisofs.h
@@ -440,7 +440,10 @@ struct iso_filesystem
 
     /**
      * Retrieve a file from its absolute path inside the filesystem.
-     *
+     * @param file
+     *     Returns a pointer to a IsoFileSource object representing the
+     *     file. It has to be disposed by iso_file_source_unref() when
+     *     no longer needed.
      * @return
      *     1 success, < 0 error (has to be a valid libisofs error code)
      *      Error codes: