This code is loaded for a picture frame page. When first loaded, it arranges to capture keystrokes.

When any of these are typed		The image is switched to
RIGHT, DOWN, PAGE-DOWN, ENTER, SPACE		next image
LEFT, UP, PAGE-UP		previous image

Details

On the frame page, the NEXT and PREV buttons have no content, but they do have id's: nextdestination and prevdestination, respectively. They look like this.

<a id="nextdestination" href="DSC04101.php" 
        class="nextbutclass"></a> 

Images for the buttons are provided in GeneralStyles.css with rules like this:

.nextbutclass:before {
    content:url("/images/NEXTbutton.png")
}
.nextbutclass:hover:before {
    content:url("/images/NEXTbuttonh.png")
}

Depending on the keystroke, the code finds either nextdestination or prevdestination. From this object it fetches the href attribute and jumps to that page by setting window.location.href.