1 files changed, 6 insertions, 0 deletions
diff --git a/lib/htmlpurifier/library/HTMLPurifier/AttrDef/URI/Host.php b/lib/htmlpurifier/library/HTMLPurifier/AttrDef/URI/Host.php
index 2156c10c6..feca469d7 100755..100644
--- a/lib/htmlpurifier/library/HTMLPurifier/AttrDef/URI/Host.php
+++ b/lib/htmlpurifier/library/HTMLPurifier/AttrDef/URI/Host.php
@@ -23,6 +23,12 @@ class HTMLPurifier_AttrDef_URI_Host extends HTMLPurifier_AttrDef
 
     public function validate($string, $config, $context) {
         $length = strlen($string);
+        // empty hostname is OK; it's usually semantically equivalent:
+        // the default host as defined by a URI scheme is used:
+        //
+        //      If the URI scheme defines a default for host, then that
+        //      default applies when the host subcomponent is undefined
+        //      or when the registered name is empty (zero length).
         if ($string === '') return '';
         if ($length > 1 && $string[0] === '[' && $string[$length-1] === ']') {
             //IPv6