tag libraries are scanned only if they appear in jar inside WEB-INF/lib or are defined in tld under WEB-INF.

The simplest scenario to explain why this is a problem: portlet 2 defines standard portlet taglib, but the classes in this file come from concrete implementations. Currently I see no way to use 2 different portals in a portable way.

Please provide a way to notify a relevant subsystem for web applications that specific module contains a .tld.