code: public UnicodeSet getTargetSet() {
          UnicodeSet result = new UnicodeSet();
          addSourceTargetSet(getFilterAsUnicodeSet(UnicodeSet.ALL_CODE_POINTS), new UnicodeSet(), result);
          return result;
      }
docs: Returns the set of all characters that may be generated as
  replacement text by this transliterator.  The default
  implementation returns the empty set.  Some subclasses may
  override this method to return a more precise result.  The
  return result is approximate in any case and is intended for
  use by tests, tools, or utilities requiring such
  meta-information.
  <p>Warning. You might expect an empty filter to always produce an empty target.
  However, consider the following:
  <pre>
  [Pp]{}[\u03A3\u03C2\u03C3\u03F7\u03F8\u03FA\u03FB] &gt; \';
  </pre>
  With a filter of [], you still get some elements in the target set, because this rule will still match. It could
  be recast to the following if it were important.
  <pre>
  [Pp]{([\u03A3\u03C2\u03C3\u03F7\u03F8\u03FA\u03FB])} &gt; \' | $1;
  </pre>
  @see #getTargetSet