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.

options = copyObj(options);
    options.shared = false;
    var markers = [markText(doc, from, to, options, type)], primary = markers[0];
    var widget = options.replacedWith;
    linkedDocs(doc, function(doc) {
      if (widget) options.replacedWith = widget.cloneNode(true);
      markers.push(markText(doc, clipPos(doc, from), clipPos(doc, to), options, type));
      for (var i = 0; i < doc.linked.length; ++i)
        if (doc.linked[i].isParent) return;
      primary = lst(markers);
    });
    return new SharedTextMarker(markers, primary);
  }
  
  function getMarkedSpanFor(spans, marker) {
    if (spans) for (var i = 0; i < spans.length; ++i) {
      var span = spans[i];
      if (span.marker == marker) return span;
    }
  }
  function removeMarkedSpan(spans, span) {
    for (var r, i = 0; i < spans.length; ++i)
      if (spans[i] != span) (r || (r = [])).push(spans[i]);
    return r;
  }
  function addMarkedSpan(line, span) {