Learning WML, and WMLScript

Events

An event in WML is simply something that can happen to some element from time to time. For example, entering a <card> element triggers an event on the <card>, and selecting an <option> from a selection list triggers an event on the <option>.

You can harness these events by binding them to a task. The usual way of doing this is with the <onevent> element. As mentioned earlier in this chapter, for simple <go> tasks you can usually make use of a simpler form: this will be mentioned when when we discuss the elements in question.

For example, the <option> element (detailed in Chapter 4) declares an item in a list of selections. When this item is selected, it triggers an onpick event on the <option> element. Suppose the element were declared without an event handler, like this:

<option>
    Purple
</option>

In this case, the onpick event is ignored, since there is no handler. If, on the other hand, the option is declared as:

<option>
    <onevent type="onpick">
        <go href="#purple"/>
    </onevent>

    Purple
</option>

the onpick event is handled by executing the <go> task, sending the browser to a new card.

The <onevent> Element

The <onevent> element declares an event binding. It can’t contain anything except a single task element that is performed when the event occurs. It may be present inside either an <option> element (see Chapter 4) or a <card> element (see Chapter 6). In either case, the <onevent> element (or elements) must be the first elements declared inside their enclosing element.

The ...