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

XForms Actions

XForms Actions are handling response to events.

The Message Action

The XForms element <message> defines a message to be displayed in the XForms user interface.

Look at this simplified example:

<input ref="fname">
<label>First Name</label>
<message level="ephemeral" event="DOMFocusIn">
Input Your First Name
</message>
</input>

In the example above, the message "Input Your First Name" should be displayed as a tool tip when the user focus in on the input field.

The event="DomFocusIn" defines the event to trigger the action.

The level="ephemeral" defines the message to be displayed as a tool tip.

Other values for the level attribute are modal and modeless, defining different types of message boxes.

The XForms element <setvalue> defines a value to be set in response to an event.

Look at this simplified example:

<input ref="size">
<label>Size</label>
<setvalue value="50" event="xforms-ready"/>
</input>

In the example above, the value 50 will be stored in the instance element <size> when the form opens.