JSF:Composite Components: How to update a form which contains a composite component from the cc

Goal: The facelet outer.xhtml contains the composite component resources/components/foocomp.xhtml. I want when I click the button in the foocomp.xhtml to update the form in order I see any errors/messages in <messages>

Attempt 1: using @form (not working)

Facelet outer.xhtml:

xmlns:comps="http://java.sun.com/jsf/composite/components">

<h:form>
   <!-- PrimeFaces messages component; equivalent to <h:messages> -->
   <p:messages showDetail="false" globalOnly="true"></p:messages>
   <comps:foocomp></comps:foocomp>
  
</h:form>

<p:commandButton action="#{fooBean.myAction()}" 
   update="@form"></p:commandButton>

Output:

javax.faces.FacesException: Cannot find component with identifier "'id_j3'" in view.

* Note: the id id_j3 is the random id given to the form as I found out.

Attempt 2: giving the form an id (not working)

Facelet outer.xhtml:

xmlns:comps="http://java.sun.com/jsf/composite/components">

<h:form id="outerForm" prependId="false">
   <!-- PrimeFaces messages component; equivalent to <h:messages> -->
   <p:messages showDetail="false" globalOnly="true"></p:messages>
   <comps:foocomp formId="outerForm"></comps:foocomp>
  
</h:form>

<composite:interface>
  <!-- the enclosed form id which will updated after an action is triggered -->
  <composite:attribute name="formId" type="java.lang.String" required="true" />
</composite:interface>

<p:commandButton action="#{fooBean.myAction()}" 
   update="#{cc.attrs.formId}">
</p:commandButton>

Output:

javax.faces.FacesException: Cannot find component with identifier "'outerForm'" in view.

Attempt 3: giving the form an id and referencing it with ':' (working!)

Facelet outer.xhtml:

xmlns:comps="http://java.sun.com/jsf/composite/components">

<h:form id="outerForm" prependId="false">
   <!-- PrimeFaces messages component; equivalent to <h:messages> -->
   <p:messages showDetail="false" globalOnly="true"></p:messages>
   <comps:foocomp formId="outerForm"></comps:foocomp>
  
</h:form>

<composite:interface>
  <!-- the enclosed form id which will updated after an action is triggered -->
  <composite:attribute name="formId" type="java.lang.String" required="true" />
</composite:interface>

<p:commandButton action="#{fooBean.myAction()}" 
   update=":#{cc.attrs.formId}"></p:commandButton>