diff --git a/web/lib/mastodon-postLength.php b/web/lib/mastodon-postLength.php
index 0202ce9..3768df4 100644
--- a/web/lib/mastodon-postLength.php
+++ b/web/lib/mastodon-postLength.php
@@ -1,5 +1,14 @@
 <?php
 
+/*
+$tldsregex has to be a string with a list (better if reverse ordered) of valid
+tlds separated by "|"; you can get such a list by adding "require gettlds.php"
+in the calling script and using it like this:
+$tldsre=gettlds($path_to_tlds_cache_file,true);
+Then you can pass the list to postLength like this: $length=postLength($post,$tldsre['tlds']);
+($tldsre['warnings'] will contain possible gettlds warnings)
+*/
+
 function postLength($post,&$tldsregex) {
 //	echo "-A-> |{$post}|\n";
 	// for some reason, mastodon seems to check tld existence only on http(s) links - see next regexp