===== Event handling =====

**Types of events**

An event is thrown by the VoiceXML platform for any number of reasons, such as a
user not responding to an input, not responding correctly, requesting help, etc. An
event is also thrown if there is a semantic error in the VoiceXML document, or when
the <throw> element is encountered. The <throw> element generates an event
(user-defined or system) and the <catch> element catches the event thrown by the
VoiceXML document, dialog, or form item.

**Throw element**

The <throw> element generates predefined or user-defined events. An example of the
use of the <throw> element is:

<code>
 <throw event="nomatch"/>
</code>

In this case, an event is generated when an input by the user is not recognized as part
of the active grammar. The attribute for the <throw> element is event, which defines
the event to be thrown.

**Catch element**

The <catch> element catches the event thrown by the VoiceXML document, dialog, or
form item. An example of the use of the <catch> element is:


<code>
 <catch event="nomatch"/>
  <throw event="event.password.invalid"/>
 </catch>
</code>

The following is a set of catch elements available:
  * <error>: catches events of type error
  * <help>: catches events if no help is available
  * <noinput>: catches events if there was no input by the user
  * <nomatch>: catches events if an input by the user is not recognized as part of the active grammar