diff --git a/devel/moth.py b/devel/moth.py
index ee13f46..6a62116 100644
--- a/devel/moth.py
+++ b/devel/moth.py
@@ -75,6 +75,7 @@ class Puzzle:
         self.authors = []
         self.answers = []
         self.scripts = []
+        self.pattern = None
         self.hint = None
         self.files = {}
         self.body = io.StringIO()
@@ -104,6 +105,8 @@ class Puzzle:
                     self.summary = val
                 elif key == 'answer':
                     self.answers.append(val)
+                elif key == 'pattern':
+                    self.pattern = val
                 elif key == 'hint':
                     self.hint = val
                 elif key == 'name':
@@ -271,6 +274,7 @@ class Puzzle:
             'hashes': self.hashes(),
             'files': files,
             'scripts': self.scripts,
+            'pattern': self.pattern,
             'body': self.html_body(),
         }
 
diff --git a/example-puzzles/example/5/puzzle.moth b/example-puzzles/example/5/puzzle.moth
index d59937e..9c3be6b 100644
--- a/example-puzzles/example/5/puzzle.moth
+++ b/example-puzzles/example/5/puzzle.moth
@@ -11,7 +11,7 @@ This page has an associated `helpers.js` script
 you can include to assist with input formatting,
 so people aren't confused about how to enter an answer.
 
-You could also write your own JavaScript to validate things
+You could also write your own JavaScript to validate things.
 
 This is just a demonstration page.
 You will probably only want one of these in a page,
diff --git a/theme/basic.css b/theme/basic.css
index 2c5170d..9614028 100644
--- a/theme/basic.css
+++ b/theme/basic.css
@@ -50,6 +50,9 @@ iframe#body {
 img {
   max-width: 100%;
 }
+input:invalid {
+  border-color: red;
+}
 #messages {
   min-height: 3em;
   border: solid black 2px;
diff --git a/theme/puzzle.js b/theme/puzzle.js
index 6ab5f07..0781287 100644
--- a/theme/puzzle.js
+++ b/theme/puzzle.js
@@ -44,11 +44,15 @@ function devel_addin(obj, e) {
   }
 }
 
+
+
 // The routine used to hash answers in compiled puzzle packages
 function djb2hash(buf) {
   let h = 5381
-  for (let c of (new TextEncoder).encode(buf)) { // JavaScript is weird.
-    h = ((h * 33) + c) & 0xffffffff
+  for (let c of (new TextEncoder).encode(buf)) { // Encode as UTF-8 and read in each byte
+    // JavaScript converts everything to a signed 32-bit integer when you do bitwise operations.
+    // So we have to do "unsigned right shift" by zero to get it back to unsigned.
+    h = (((h * 33) + c) & 0xffffffff) >>> 0
   }
   return h
 }
@@ -132,6 +136,11 @@ function loadPuzzle(categoryName, points, puzzleId) {
     for (let se of doc.querySelectorAll("[src],[href]")) {
       se.outerHTML = se.outerHTML.replace(/(src|href)="([^/]+)"/i, "$1=\"" + base + "$2\"")
     }
+    
+    // If a validation pattern was provided, set that
+    if (obj.pattern) {
+      document.querySelector("#answer").pattern = obj.pattern
+    }
 
     // Replace puzzle children with what's in `doc`
     Array.from(puzzle.childNodes).map(e => e.remove())