Version control

The menu frame on the left will be either of two files, depending on whether the browser recognizes the language="javascript1.1"

Those older browsers that cannot support "image switching" (rollover buttons) will retain the left.html file, which contains a simple column of buttons, whereas the browsers that "see" the script block labeled "language=javascript1.1" will encounter the "replace" mechanism in that script. The replace mechanism bounces the left hand frame to a second html page that contains javascript rollover events, image switching, etc. This is an effective way to maintain version control without testing to see who made the browser.

Those of you with new browsers will have a hard time looking at the menu_js1.html, so I am reproducing its script here:
<script language="JavaScript1.1">