diff --git a/ChangeLog b/ChangeLog
index 7fbd7282..53127bd8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,8 @@
 <pre>
 2007-07-02:
 	* version 0.5
+	* Ctrl-U/Ctrl-D for scrolling the window up/down and the associated
+	'scroll' option
 	* files in ~/.vimperator/plugin/ are auto-sourced
 	* :winopen support (multiple windows still very very experimental)
 	* 'activate' option implemented
diff --git a/chrome/content/vimperator/buffers.js b/chrome/content/vimperator/buffers.js
index cfd265b8..6d398ee3 100644
--- a/chrome/content/vimperator/buffers.js
+++ b/chrome/content/vimperator/buffers.js
@@ -75,6 +75,11 @@ function Buffer() //{{{
         return window.content.document.location.href;
     });
 
+    this.__defineGetter__("pageHeight", function()
+    {
+        return getBrowser().mPanelContainer.boxObject.height; // FIXME: best way to do this?
+    });
+
     this.__defineGetter__("textZoom", function()
     {
         return zoom_manager.textZoom;
diff --git a/chrome/content/vimperator/commands.js b/chrome/content/vimperator/commands.js
index 0c856761..20754eac 100644
--- a/chrome/content/vimperator/commands.js
+++ b/chrome/content/vimperator/commands.js
@@ -892,7 +892,7 @@ function Commands() //{{{
                             if (oper == '-') num = cur_val - num;
                             // FIXME
                             if (option.validator != null && option.validator.call(this, num) == false)
-                                vimperator.echoerr("E521: Number required after =: " + option.name + "=" + val);
+                                vimperator.echoerr("E474: Invalid argument: " + option.name + "=" + val); // FIXME: need to be able to specify unique parse error messages
                             else // all checks passed, execute option handler
                                 option.value = num;
                         }
diff --git a/chrome/content/vimperator/mappings.js b/chrome/content/vimperator/mappings.js
index cc24dae4..12cc045d 100644
--- a/chrome/content/vimperator/mappings.js
+++ b/chrome/content/vimperator/mappings.js
@@ -308,7 +308,7 @@ function Mappings() //{{{
         function(count) { vimperator.buffer.shiftFrameFocus(count > 1 ? count : 1, true); },
         {
             short_help: "Focus next frame",
-            help: "Transfers keyboard focus to the [count]th next frame in order. The newly focused frame is briefly colored red.",
+            help: "Transfers keyboard focus to the <code class=\"argument\">[count]</code>th next frame in order. The newly focused frame is briefly colored red.",
             flags: Mappings.flags.COUNT
         }
     ));
@@ -316,7 +316,7 @@ function Mappings() //{{{
         function(count) { vimperator.buffer.shiftFrameFocus(count > 1 ? count : 1, false); },
         {
             short_help: "Focus previous frame",
-            help: "Transfers keyboard focus to the [count]th previous frame in order. The newly focused frame is briefly colored red.",
+            help: "Transfers keyboard focus to the <code class=\"argument\">[count]</code>th previous frame in order. The newly focused frame is briefly colored red.",
             flags: Mappings.flags.COUNT
         }
     ));
@@ -673,6 +673,39 @@ function Mappings() //{{{
             flags: Mappings.flags.COUNT
         }
     ));
+    function getScrollSize(count)
+    {
+        var lines;
+
+        if (count > 1)
+            vimperator.options["scroll"] = count;
+
+        if (vimperator.options["scroll"] == 0) // the default value of half a page
+            // FIXME: when updating the scroll methods in v.buffer!
+            lines = vimperator.buffer.pageHeight / (2 * 20); // NOTE: a line is currently 20 pixels rather than a true line.
+        else
+            lines = vimperator.options["scroll"];
+
+        return lines;
+    }
+    addDefaultMap(new Map(vimperator.modes.NORMAL, ["<C-d>"],
+        function(count) { vimperator.buffer.scrollRelative(0, getScrollSize(count)); },
+        {
+            short_help: "Scroll window downwards in the buffer",
+            help: "The number of lines is set by the <code class=\"option\">'scroll'</code> option which defaults to half a page. " +
+                  "If <code class=\"argument\">[count]</code> is given <code class=\"option\">'scroll'</code> is first set to this value.",
+            flags: Mappings.flags.COUNT
+        }
+    ));
+    addDefaultMap(new Map(vimperator.modes.NORMAL, ["<C-u>"],
+        function(count) { vimperator.buffer.scrollRelative(0, -getScrollSize(count)); },
+        {
+            short_help: "Scroll window upwards in the buffer",
+            help: "The number of lines is set by the <code class=\"option\">'scroll'</code> option which defaults to half a page. " +
+                  "If <code class=\"argument\">[count]</code> is given <code class=\"option\">'scroll'</code> is first set to this value.",
+            flags: Mappings.flags.COUNT
+        }
+    ));
     addDefaultMap(new Map(vimperator.modes.NORMAL, ["l", "<Right>"],
         function(count) { vimperator.buffer.scrollRelative(count > 1 ? count : 1, 0); },
         {
@@ -682,14 +715,14 @@ function Mappings() //{{{
             flags: Mappings.flags.COUNT
         }
     ));
-    addDefaultMap(new Map(vimperator.modes.NORMAL, ["<C-b>", "<C-u>", "<PageUp>", "<S-Space>"],
+    addDefaultMap(new Map(vimperator.modes.NORMAL, ["<C-b>", "<PageUp>", "<S-Space>"],
         function() { goDoCommand('cmd_scrollPageUp'); },
         {
             short_help: "Scroll up a full page of the current document",
             help: "No count support for now."
         }
     ));
-    addDefaultMap(new Map(vimperator.modes.NORMAL, ["<C-f>", "<C-d>", "<PageDown>", "<Space>"],
+    addDefaultMap(new Map(vimperator.modes.NORMAL, ["<C-f>", "<PageDown>", "<Space>"],
         function() { goDoCommand('cmd_scrollPageDown'); },
         {
             short_help: "Scroll down a full page of the current document",
diff --git a/chrome/content/vimperator/options.js b/chrome/content/vimperator/options.js
index 67a3b750..eff0acf9 100644
--- a/chrome/content/vimperator/options.js
+++ b/chrome/content/vimperator/options.js
@@ -421,6 +421,14 @@ function Options() //{{{
             validator: function (value) { if (value>=1 && value <=50) return true; else return false; }
         }
     ));
+    addOption(new Option(["scroll", "scr"], "number",
+        {
+            short_help: "Number of lines to scroll with <code class=\"mapping\">C-u</code> and <code class=\"mapping\">C-d</code> commands",
+            help: "TODO",
+            default_value: 0,
+            validator: function (value) { if (value >= 0) return true; else return false; }
+        }
+    ));
     addOption(new Option(["showmode", "smd"], "boolean",
         {
             short_help: "Show the current mode in the command line",
@@ -436,7 +444,7 @@ function Options() //{{{
                   "<li><b>1</b>: Show the link in the status line</li>" +
                   "<li><b>2</b>: Show the link in the command line</li></ul>",
             default_value: 1,
-            validator: function (value) { if (value>=0 && value <=2) return true; else return false; }
+            validator: function (value) { if (value >= 0 && value <= 2) return true; else return false; }
         }
     ));
     addOption(new Option(["showtabline", "stal"], "number",