|The action to take when this command is invoked.
If the value is an expression, it is expected to be a method binding EL expression that identifies
an action method. An action method accepts no parameters and has a String return value, called the
action outcome, that identifies the next view displayed. The phase that this event is fired in
can be controlled via the immediate attribute.
If the value is a string literal, it is treated as a navigation outcome for the current view. This
is functionally equivalent to a reference to an action method that returns the string literal.