addJavaScriptAtPosition, addStyleSheet, ... doesn't work

hi

in my custom component

1. this generates no link tag (no change in generated html):
AddResource ar = AddResourceFactory.getInstance(context);
ar.addStyleSheet(context, AddResource.HEADER_BEGIN, "/css/myComponent.css");

2. this generates script tag in the place of first use of component but not in the header as expected
ar.addJavaScriptAtPosition(context, AddResource.HEADER_BEGIN, "/js/myComponent.js");

I have configured ExtensionFilter of course.
I was also trying with:
<context-param>
<param-name>org.apache.myfaces.ADD_RESOURCE_CLASS</param-name>
<param-value>org.apache.myfaces.component.html.util.StreamingAddResource</param-value>
</context-param>

and using t:document, t:documentHeader, t:documentBody ...

allways the same result

thanks