diff --git a/docs/bitmasks.js b/docs/bitmasks.js
new file mode 100644
index 000000000..e2253ff77
--- /dev/null
+++ b/docs/bitmasks.js
@@ -0,0 +1,40 @@
+
+var cat;
+
+function CheckCharacters(text,allowed) {
+  for (var i = 0; i < text.length; ++i) {
+    if(allowed.indexOf(text.charAt(i))<0 ) {
+      return false;
+    }
+  }
+  return true;
+}
+
+function Calc() {
+  var input = document.getElementById("input").value*1;
+  if(CheckCharacters(input,"0123456789")) cat=input;
+
+  for(var i=0;i<BIT_COUNT;++i)
+    Mark(i);
+}
+
+function Mark(bit) {
+  if((1<<bit) & cat) {
+    if(!(bit%2))
+      document.getElementById(PREFIX+bit).className="mark";
+    else
+      document.getElementById(PREFIX+bit).className="darkmark";
+  }
+  else {
+    if(!(bit%2))
+      document.getElementById(PREFIX+bit).className="";
+    else
+      document.getElementById(PREFIX+bit).className="dark";
+  }
+}
+
+function Switch(bit) {
+  cat = cat ^ (1 << bit);
+  Mark(bit);
+  document.getElementById("input").value = cat;
+}
\ No newline at end of file