The Reference documentation has this line in Section 1.2.2. How it works, where it describes how the Registrastration example works:
When the form is submitted, JSF asks Seam to resolve the variable named user.
<h:panelGrid columns="2">
Username: <h:inputText value="#{user.username}" required="true"/>
Real Name: <h:inputText value="#{user.name}" required="true"/>
Password: <h:inputSecret value="#{user.password}" required="true"/>
</h:panelGrid>No, its because EL provides an extension point called ELResolver.