code: public void pushOut (String pattern)
      {
          Pattern pat = makePattern(pattern);
          Iterator<String> i = _imports.iterator();
          while (i.hasNext()) {
              String imp = i.next();
              if (pat.matcher(imp).matches()) {
                  i.remove();
                  _pushed.add(imp);
                  return;
              }
          }
          _pushed.add(null);
      }
docs: Temporarily remove one import matching the given pattern. The most recently pushed pattern
  can be re-added using <code>popIn</code>. If there is no match, a null value is pushed so
  that popIn can still be called.
  @param pattern to match