Isindex

The void HTML   element has been deprecated since HTML4 for its poorly supported method for providing a searchable index related to the current document. Originally, it was intended (by the W3C) that this element should be placed inside the  of the document, but most browsers allowed it to be used anywhere in the document. This element has been deprecated in favor of.

Attributes
See Global HTML Attributes.
 * Global Attributes

HTML example:

That produces:

Without the  attribute, it produces: