From: <Juergen.Zimmermann_at_HS-Karlsruhe.de>
Date: Tue, 26 May 2009 06:16:53 +0200

It's absolutely easy, e.g.:

<h:form id="myForm">
        <h:inputText id="lastname" value="#{bean.customer.lastname}">
                <f:ajax event="blur" render="myForm:errorLastname"/>
        </h:inputText>
        <h:messages id="errorLastname" for="lastname"/>