Right now we use codemirror's JavaScript mode on the website but there's a JSX mode now so we should start using that instead.

this.lines = [];
    this.type = type;
    this.doc = doc;
  }
  CodeMirror.TextMarker = TextMarker;
  eventMixin(TextMarker);
  TextMarker.prototype.clear = function() {
    if (this.explicitlyCleared) return;
    var cm = this.doc.cm, withOp = cm && !cm.curOp;
    if (withOp) startOperation(cm);
    if (hasHandler(this, "clear")) {
      var found = this.find();
      if (found) signalLater(this, "clear", found.from, found.to);
    }
    var min = null, max = null;
    for (var i = 0; i < this.lines.length; ++i) {
      var line = this.lines[i];
      var span = getMarkedSpanFor(line.markedSpans, this);
      if (span.to != null) max = lineNo(line);
      line.markedSpans = removeMarkedSpan(line.markedSpans, span);
      if (span.from != null)
        min = lineNo(line);
      else if (this.collapsed && !lineIsHidden(this.doc, line) && cm)
        updateLineHeight(line, textHeight(cm.display));
    }
    if (cm && this.collapsed && !cm.options.lineWrapping) for (var i = 0; i < this.lines.length; ++i) {
      var visual = visualLine(cm.doc, this.lines[i]), len = lineLength(cm.doc, visual);
      if (len > cm.display.maxLineLength) {
        cm.display.maxLine = visual;