<ISINDEX PROMPT="Enter Glossary Term" 
            ACTION="http://url_to_program/prog">

HTML 4.0 introduces the additional attribute PROMPT, which allow the author to specify the prompt string for the ISINDEX query box. This is supported by most current browsers. Many also support an ACTION attribute, which lets an author specify the URL to which the query data should be sent.

Kind of the poor man's <form>. I have never seen this in the wild, which I was I put it there.