I'm seeing some console errors coming from this line.

```
Uncaught TypeError: Cannot read property 'line' of undefined codemirror.js:2492
clipPos codemirror.js:2492
window.CodeMirror.createObj.markText codemirror.js:4846
(anonymous function) codemirror.js:4948
showPreview main.js:153
(anonymous function) main.js:615
```