where is method-signature="java.lang.String action()" coming from?

[Himai Minh]

Hi, in ch 9 of Core JSF,
in icon.xhtml:

 <composite:interface>
          <composite:attribute name ="actionMethod" method-signature="java.lang.String action()" />
 </composite:interface>

In Welcome.xhtml that uses the composite defined in icon.xhtml:

  <util:icon image="...." actionMethod="#{user.logout}"..... />

I don't know how it comes up with this method-signature. I don't see any method called action() in any of the managed bean.

[Himai Minh]

Let me answer my own question.
The method-signature is the refering to the user bean's logout method. This method returns a String and accept no parameter.
If I changed the method-signature into "java.lang.String logout()". It still works.