diff --git a/src/lib/codemirror/addon/selection/active-line.js b/src/lib/codemirror/addon/selection/active-line.js
new file mode 100644
index 000000000..aa295d0d8
--- /dev/null
+++ b/src/lib/codemirror/addon/selection/active-line.js
@@ -0,0 +1,72 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: http://codemirror.net/LICENSE
+
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") // CommonJS
+    mod(require("../../lib/codemirror"));
+  else if (typeof define == "function" && define.amd) // AMD
+    define(["../../lib/codemirror"], mod);
+  else // Plain browser env
+    mod(CodeMirror);
+})(function(CodeMirror) {
+  "use strict";
+  var WRAP_CLASS = "CodeMirror-activeline";
+  var BACK_CLASS = "CodeMirror-activeline-background";
+  var GUTT_CLASS = "CodeMirror-activeline-gutter";
+
+  CodeMirror.defineOption("styleActiveLine", false, function(cm, val, old) {
+    var prev = old == CodeMirror.Init ? false : old;
+    if (val == prev) return
+    if (prev) {
+      cm.off("beforeSelectionChange", selectionChange);
+      clearActiveLines(cm);
+      delete cm.state.activeLines;
+    }
+    if (val) {
+      cm.state.activeLines = [];
+      updateActiveLines(cm, cm.listSelections());
+      cm.on("beforeSelectionChange", selectionChange);
+    }
+  });
+
+  function clearActiveLines(cm) {
+    for (var i = 0; i < cm.state.activeLines.length; i++) {
+      cm.removeLineClass(cm.state.activeLines[i], "wrap", WRAP_CLASS);
+      cm.removeLineClass(cm.state.activeLines[i], "background", BACK_CLASS);
+      cm.removeLineClass(cm.state.activeLines[i], "gutter", GUTT_CLASS);
+    }
+  }
+
+  function sameArray(a, b) {
+    if (a.length != b.length) return false;
+    for (var i = 0; i < a.length; i++)
+      if (a[i] != b[i]) return false;
+    return true;
+  }
+
+  function updateActiveLines(cm, ranges) {
+    var active = [];
+    for (var i = 0; i < ranges.length; i++) {
+      var range = ranges[i];
+      var option = cm.getOption("styleActiveLine");
+      if (typeof option == "object" && option.nonEmpty ? range.anchor.line != range.head.line : !range.empty())
+        continue
+      var line = cm.getLineHandleVisualStart(range.head.line);
+      if (active[active.length - 1] != line) active.push(line);
+    }
+    if (sameArray(cm.state.activeLines, active)) return;
+    cm.operation(function() {
+      clearActiveLines(cm);
+      for (var i = 0; i < active.length; i++) {
+        cm.addLineClass(active[i], "wrap", WRAP_CLASS);
+        cm.addLineClass(active[i], "background", BACK_CLASS);
+        cm.addLineClass(active[i], "gutter", GUTT_CLASS);
+      }
+      cm.state.activeLines = active;
+    });
+  }
+
+  function selectionChange(cm, sel) {
+    updateActiveLines(cm, sel.ranges);
+  }
+});