CodeMirror: Diff mode

diff --git a/index.html b/index.html
index c1d9156..7764744 100644
--- a/index.html
+++ b/index.html
@@ -95,7 +95,8 @@ StringStream.prototype = {
     <script>
       var editor = CodeMirror.fromTextArea(document.getElementById("code"), {
         lineNumbers: true,
-        autoMatchBrackets: true
+        autoMatchBrackets: true,
+      onGutterClick: function(x){console.log(x);}
       });
     </script>
   </body>
diff --git a/lib/codemirror.js b/lib/codemirror.js
index 04646a9..9a39cc7 100644
--- a/lib/codemirror.js
+++ b/lib/codemirror.js
@@ -399,10 +399,16 @@ var CodeMirror = (function() {
     }
 
     function onMouseDown(e) {
-      var start = posFromMouse(e), last = start;
+      var start = posFromMouse(e), last = start, target = e.target();
       if (!start) return;
       setCursor(start.line, start.ch, false);
       if (e.button() != 1) return;
+      if (target.parentNode == gutter) {
+        if (options.onGutterClick)
+          options.onGutterClick(indexOf(gutter.childNodes, target) + showingFrom);
+        return;
+      }
+
       if (!focused) onFocus();
 
       e.stop();
@@ -808,7 +814,7 @@ var CodeMirror = (function() {
       for (var i = showingFrom; i < showingTo; ++i) {
         var marker = lines[i].gutterMarker;
         if (marker) html.push('<div class="' + marker.style + '">' + htmlEscape(marker.text) + '</div>');
-        else html.push("<div>" + (options.lineNumbers ? i + 1 : "\u00a0") + "</div>");
+        else html.push("<div>" + (options.lineNumbers ? i + options.firstLineNumber : "\u00a0") + "</div>");
       }
       gutter.style.display = "none"; // TODO test whether this actually helps
       gutter.innerHTML = html.join("");
@@ -1371,10 +1377,8 @@ var CodeMirror = (function() {
         if (option == "parser") setParser(value);
         else if (option === "lineNumbers") setLineNumbers(value);
         else if (option === "gutter") setGutter(value);
-        else if (option === "readOnly") options.readOnly = value;
-        else if (option === "indentUnit") {options.indentUnit = indentUnit = value; setParser(options.parser);}
-        else if (/^(?:enterMode|tabMode|indentWithTabs|readOnly|autoMatchBrackets|undoDepth)$/.test(option)) options[option] = value;
-        else throw new Error("Can't set option " + option);
+        else if (option === "indentUnit") {options.indentUnit = value; setParser(options.parser);}
+        else options[option] = value;
       },
       cursorCoords: cursorCoords,
       undo: operation(undo),
@@ -1402,7 +1406,8 @@ var CodeMirror = (function() {
       replaceRange: operation(replaceRange),
 
       operation: function(f){return operation(f)();},
-      refresh: function(){updateDisplay([{from: 0, to: lines.length}]);}
+      refresh: function(){updateDisplay([{from: 0, to: lines.length}]);},
+      getInputField: function(){return input;}
     };
     return instance;
   }
@@ -1420,6 +1425,7 @@ var CodeMirror = (function() {
     readOnly: false,
     onChange: null,
     onCursorActivity: null,
+    onGutterClick: null,
     autoMatchBrackets: false,
     workTime: 200,
     workDelay: 300,

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