In an item type plug-in you create an item with the possibility to extend its functionality. To demonstrate this, we will make a text field with a tooltip. This functionality is already available in APEX 4.0 by adding the following code to the HTML form element attributes text field in the Element section of the text field:
onmouseover="toolTip_enable(event,this,'A tooltip')"
But you have to do this for every item that should contain a tooltip. This can be made more easily by creating an item type plug-in with a built-in tooltip. And if you create an item of type plug-in, you will be asked to enter some text for the tooltip.
For this recipe you can use an existing page, with a region in which you can put some text items.