jsf 2 - Why is not possible passing event name as argument to a composite component in JSF 2? -

why can't pass event name argument composite component bean in jsf 2.

this works:

<f:ajax event="click"         render="#{cc.attrs.ajaxrender}"         execute="#{cc.attrs.ajaxexecute}"         immediate="#{cc.attrs.immediate}"/> 

this doesn't:

<f:ajax event="#{cc.attrs.itemevent}"         render="#{cc.attrs.ajaxrender}"         execute="#{cc.attrs.ajaxexecute}"         immediate="#{cc.attrs.immediate}"/> 

question is: why? note: eventname defined in cc:interface following:

<composite:attribute name="itemevent" default="click"/>