Swap-previous escapes parent in html

Given this content:

```html
<parent>
  <child>1</child>
  <child>2</child>
</parent>
```

Calling `codeBlocks.moveUp` on `<child>1</child>` causes it to escape from parent:

```html
<child>1</child>
<parent>
  <child>2</child>
</parent>
```

Expected behavior is to not allow this.