if you include the taglib directive in your .jsp code completion works automatically.
<%@ taglib uri="....mytaguri...." prefix="mytag" %>
it's even working if you have this taglib directive in a kind of header file that bis included in your .jsp lke that:
<%@ include file="../common/taglibincludes.jspf" %>
the only problem is that the path mustn't start with /
<%@ include file="/common/taglibincludes.jspf" %>
it's NOT working!!!!