<appearance/>

<submit label="button.label.perform_action" action="performAction">
  <appearance function="buttonAppearance"/>
</submit>

button.label.perform_action=Perform action

DSL_APPEARANCE buttonAppearance() {

	// Preference to disabled appearance 
    if(disableButton()) {
		return DSL_APPEARANCE.Disable;
	}
	else if(highlightButton()) {
		return DSL_APPEARANCE.Highlight;
	}

	// returning null here implies default appearance
	// equivalent to return DSL_APPEARANCE.Default
	return null;
}