Specifies alternate text to display if a specified image is not available. Available at design time.
Remarks
The alternative text also displays while an image is loading and behaves as a Tooltip in the Microsoft® Internet Explorer 4.0 browser.
If you want to display an image on a button, specify a value for the Image property and leave the Caption property empty.
When you specify an image, it is a good idea to specify a value for the AltText property in case the image is not available when a user browses the page.
This property is mapped to the Alternate text box on the General Tab of the Button Properties dialog box.