From http://www.w3schools.com (Copyright Refsnes Data)

WML <onevent> tag

The <onevent> tag contains code to be executed when one of the following events occurs: onenterbackward, onenterforward, onpick, ontimer.

Syntax

<onevent type="type">
..code..
</onevent>

Attributes

Attribute	Value	Description
type	onenterbackward onenterforward onpick ontimer	REQUIRED. Specifies the type of the "onevent" element. onenterbackward - Triggered when a <prev> goes to a previous card onenteredforward - Triggered when a <go> goes to a card onpick - Triggered when an item is selected/unselected ontimer - Triggered when a timer expires
class	cdata	Sets a class name for the element. The class name is case sensitive. An element can be connected to multiple classes. Multiple class names within the class attribute are separated by white space
id	id	Sets a unique name for the element

Examples

The example below uses the <onevent> tag to always navigate to card1 when an onenterbackward event occurs:

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>
<template>
 <onevent type="onenterbackward">
  <go href="#card1"/>
 </onevent>
</template>

<card id="card1" title="Card 1">
<p>
 Hello World!
</p>
</card>

<card id="card2" title="Card 2">
<p>
 From W3Schools!
</p>
</card>
</wml>

Complete WML Reference