1 files changed, 6 insertions, 1 deletions
diff --git a/lib/js/urweb.js b/lib/js/urweb.js
index 251f64ba..7349d2bf 100644
--- a/lib/js/urweb.js
+++ b/lib/js/urweb.js
@@ -464,10 +464,15 @@ function pflo(s) {
 }
 
 function uf(s) {
-  return escape(s).replace(new RegExp ("/", "g"), "%2F").replace(new RegExp ("\\+", "g"), "%2B");
+  if (s.length == 0)
+    return "_";
+  return (s[0] == '_' ? "_" : "")
+        + escape(s).replace(new RegExp ("/", "g"), "%2F").replace(new RegExp ("\\+", "g"), "%2B");
 }
 
 function uu(s) {
+  if (s.length > 0 && s[0] == '_')
+    s = s.substring(1);
   return unescape(s.replace(new RegExp ("\\+", "g"), " "));
 }