code: public static void registerAlias(String aliasID, String realID) {
          registry.put(aliasID, realID, true);
      }
docs: Register an ID as an alias of another ID.  Instantiating
  alias ID produces the same result as instantiating the original ID.
  This is generally used to create short aliases of compound IDs.
  
  <p>Because ICU may choose to cache Transliterator objects internally, this must
  be called at application startup, prior to any calls to
  Transliterator.getInstance to avoid undefined behavior.
  
  @param aliasID The new ID being registered.
  @param realID The existing ID that the new ID should be an alias of.