code: public String parseAndRender(String pExpressionString)
              throws ELException {
          Object val = parseExpressionString(pExpressionString);
          if (val instanceof String) {
              return (String) val;
          } else if (val instanceof Expression) {
              return "${" + ((Expression) val).getExpressionString() + "}";
          } else if (val instanceof ExpressionString) {
              return ((ExpressionString) val).getExpressionString();
          } else {
              return "";
          }
      }
docs: Parses the given expression string, then converts it back to a
  String in its canonical form.  This is used to test parsing.