Unzip and copy the hiddentext directory into the /moodle/filter/ directory then navigate to Site Administration | Modules | Filters | Manage Filters and click on the eye icon in the row labeled Hiddentext.

With the filter in place, text can be marked as hidden text by placing filter tags around it. In a WYSIWYG editor [span] and [div] tags can be used. A [span] tag can be used within a sentence and a [div] tag hides a section of a paragraph or more.

If you wanted to ask a question and temporarily hide the answer you could write content as follows:

Before the hidden content there is a filter tag:

[span filter="hidden text"]

The end of the hidden content is followed by a closing filter tag:

[/span]

When the text is parsed by the filter, the hidden text is replaced by an eye icon.

Clicking on the icon reveals the hidden text.

Clicking the icon again re-hides the content.

The icon itself is meaningful, but not necessarily intuitive. It is possible to add a label to accompany the icon. This is achieved by adding a desc attribute to the initial filter tag.

The label is then rendered next to the icon as follows.

The Hidden Text filter uses the YUI library to hide and reveal text. This is how it achieves a fade effect.

The Hidden Text filter is not limited to questions and answers. It can be used to hide content of any kind. Here are some applications: