code: public static String stripMacro(String input) {
  
          if (isMacro(input)) {
              return input.substring(2, input.length() - 1);
          }
          return null;
      }
docs: Strips the macro delimiters from the given input,
  for example <code>%(key)</code> or <code>${key}</code> becomes <code>key</code>.<p>
  
  In case the input is not a macro, <code>null</code> is returned.<p>
  
  @param input the input to strip
  
  @return the macro stripped from the input, or <code>null</code>