Sometimes you may want to warn you user of something, such as a plug-in they may need, for example, and you can do this with an error pop-up message
Making a Pop-Up Message
1. In the behaviors panel, select the browser version you are planning to prepare
for.
2. In the document window, select the object you want add the behavior to. If it is the whole page, select the whole body tag, opening to closing, or click on the work <body> in the bottom of the document window.
*note: If you are using a link that doesn't need to go anywhere, put in a "#"
symbol in the URL box, or the word "Javascript:;"
ex.
3. In the Behaviors Panel select the Pop-Up Message action.
4. In the dialog box that follows, type in your message and click o.k.
5. In the Behaviors Panel select an event from the pull down (ex. onMouseDown)
