code: public static Properties merge(Properties properties, File extra) throws IOException {
          Properties props = load(extra);
          return mergeAndOverrideExisting(properties, props);
      }
docs: Utility method to merge instructions from the given file into the given set of instructions. The instructions
  from the given file override the existing instructions (when both contain the same instruction)
  
  @param properties the current instructions
  @param extra      the file
  @return the new set of instructions
  @throws IOException if the file cannot be read