How can I [cloze](http://en.wikipedia.org/wiki/Cloze_test) some text in an HTML document? Some marked text is hidden, replaced with an underline of exactly the same length as the original text and all of the words in the sentence should appear in precisely the same places they would appear had there not been a cloze. E.g.:

```
Once upon a time there ______ a cat.

```

The word to be clozed might be marked like this:

```
Once upon a time there <div class="cloze">lived</div> a cat.

```

Is there some way to hide the text and create an underline of exactly the same length?