diff --git a/website/playground/Playground.js b/website/playground/Playground.js
index 4192e112..1c9492db 100644
--- a/website/playground/Playground.js
+++ b/website/playground/Playground.js
@@ -121,7 +121,7 @@ class Playground extends React.Component {
                   <div className="editors">
                     <InputPanel
                       mode={util.getCodemirrorMode(options.parser)}
-                      rulerColumn={options.printWidth}
+                      ruler={options.printWidth}
                       value={content}
                       placeholder={getCodeSample(options.parser)}
                       onChange={this.setContent}
@@ -135,13 +135,13 @@ class Playground extends React.Component {
                     <OutputPanel
                       mode={util.getCodemirrorMode(options.parser)}
                       value={formatted}
-                      rulerColumn={options.printWidth}
+                      ruler={options.printWidth}
                     />
                     {editorState.showSecondFormat ? (
                       <OutputPanel
                         mode={util.getCodemirrorMode(options.parser)}
                         value={getSecondFormat(formatted, debug.reformatted)}
-                        rulerColumn={options.printWidth}
+                        ruler={options.printWidth}
                       />
                     ) : null}
                   </div>
diff --git a/website/playground/panels.js b/website/playground/panels.js
index 72ac0f97..fd5440a0 100644
--- a/website/playground/panels.js
+++ b/website/playground/panels.js
@@ -7,12 +7,13 @@ class CodeMirrorPanel extends React.Component {
     this._textareaRef = React.createRef();
     this._codeMirror = null;
     this._cached = "";
+    this._overlay = null;
     this.handleChange = this.handleChange.bind(this);
   }
 
   componentDidMount() {
     const options = Object.assign({}, this.props);
-    delete options.rulerColumn;
+    delete options.ruler;
     delete options.rulerColor;
     delete options.value;
     delete options.onChange;
@@ -26,6 +27,7 @@ class CodeMirrorPanel extends React.Component {
     this._codeMirror.on("change", this.handleChange);
 
     this.updateValue(this.props.value || "");
+    this.updateOverlay();
   }
 
   componentWillUnmount() {
@@ -35,6 +37,13 @@ class CodeMirrorPanel extends React.Component {
   componentDidUpdate(prevProps) {
     if (this.props.readOnly && this.props.value !== this._cached) {
       this.updateValue(this.props.value);
+      this.updateOverlay();
+    }
+    if (
+      this.props.overlayStart !== prevProps.overlayStart ||
+      this.props.overlayEnd !== this.props.overlayEnd
+    ) {
+      this.updateOverlay();
     }
     if (this.props.mode !== prevProps.mode) {
       this._codeMirror.setOption("mode", this.props.mode);
@@ -42,7 +51,7 @@ class CodeMirrorPanel extends React.Component {
     if (this.props.placeholder !== prevProps.placeholder) {
       this._codeMirror.setOption("placeholder", this.props.placeholder);
     }
-    if (this.props.rulerColumn !== prevProps.rulerColumn) {
+    if (this.props.ruler !== prevProps.ruler) {
       this._codeMirror.setOption("rulers", [makeRuler(this.props)]);
     }
   }
@@ -52,6 +61,20 @@ class CodeMirrorPanel extends React.Component {
     this._codeMirror.setValue(value);
   }
 
+  updateOverlay() {
+    if (!this.props.readOnly) {
+      if (this._overlay) {
+        this._codeMirror.removeOverlay(this._overlay);
+      }
+      const [start, end] = getIndexPosition(this.props.value, [
+        this.props.overlayStart,
+        this.props.overlayEnd
+      ]);
+      this._overlay = createOverlay(start, end);
+      this._codeMirror.addOverlay(this._overlay);
+    }
+  }
+
   handleChange(doc, change) {
     if (change.origin !== "setValue") {
       this._cached = doc.getValue();
@@ -68,8 +91,56 @@ class CodeMirrorPanel extends React.Component {
   }
 }
 
+function getIndexPosition(text, indexes) {
+  indexes = indexes.slice().sort();
+  let line = 0;
+  let count = 0;
+  let lineStart = 0;
+  const result = [];
+
+  while (indexes.length) {
+    const index = indexes.shift();
+
+    while (count < index && count < text.length) {
+      count++;
+      if (text[count] === "\n") {
+        line++;
+        lineStart = count;
+      }
+    }
+
+    result.push({ line, pos: count - lineStart });
+  }
+
+  return result;
+}
+
+function createOverlay(start, end) {
+  return {
+    token(stream) {
+      const line = stream.lineOracle.line;
+
+      if (line < start.line || line > end.line) {
+        stream.skipToEnd();
+      } else if (line === start.line && stream.pos < start.pos) {
+        stream.pos = start.pos;
+      } else if (line === end.line) {
+        if (stream.pos < end.pos) {
+          stream.pos = end.pos;
+          return "searching";
+        } else {
+          stream.skipToEnd();
+        }
+      } else {
+        stream.skipToEnd();
+        return "searching";
+      }
+    }
+  };
+}
+
 function makeRuler(props) {
-  return { column: props.rulerColumn, color: props.rulerColor };
+  return { column: props.ruler, color: props.rulerColor };
 }
 
 export function InputPanel(props) {
@@ -82,6 +153,8 @@ export function InputPanel(props) {
       showCursorWhenSelecting={true}
       tabWidth={2}
       rulerColor="#eeeeee"
+      rangeStart={5}
+      rangeEnd={25}
       {...props}
     />
   );
@@ -108,3 +181,31 @@ export function DebugPanel({ value }) {
     />
   );
 }
+
+function stringify(obj, replacer, spaces, cycleReplacer) {
+  return JSON.stringify(obj, serializer(replacer, cycleReplacer), spaces);
+}
+
+function serializer(replacer, cycleReplacer) {
+  var stack = [],
+    keys = [];
+
+  if (cycleReplacer == null)
+    cycleReplacer = function(key, value) {
+      if (stack[0] === value) return "[Circular ~]";
+      return (
+        "[Circular ~." + keys.slice(0, stack.indexOf(value)).join(".") + "]"
+      );
+    };
+
+  return function(key, value) {
+    if (stack.length > 0) {
+      var thisPos = stack.indexOf(this);
+      ~thisPos ? stack.splice(thisPos + 1) : stack.push(this);
+      ~thisPos ? keys.splice(thisPos, Infinity, key) : keys.push(key);
+      if (~stack.indexOf(value)) value = cycleReplacer.call(this, key, value);
+    } else stack.push(value);
+
+    return replacer == null ? value : replacer.call(this, key, value);
+  };
+}