Add a keyboard event listener to the element (focus or focusin) which will trigger the same functionality as the mouse event.
Engine scans for elements having a mouseenter event, but no corresponding keyboard event (focus or focusin).
Using both keyboard-specific and mouse-specific events together ensures that content can be operated by a wide range of devices. For example, a script may perform the same action when a focus is detected that is performed when the mouse pointer enters the element.
<a href="menu.php" onmouseover="swapImageOn('menu')" onfocus="swapImageOn('menu')"