code: public ConfigParseOptions setSyntax(ConfigSyntax syntax) {
          if (this.syntax == syntax)
              return this;
          else
              return new ConfigParseOptions(syntax, this.originDescription, this.allowMissing,
                      this.includer, this.classLoader);
      }
docs: Set the file format. If set to null, try to guess from any available
  filename extension; if guessing fails, assume {@link ConfigSyntax#CONF}.
  
  @param syntax
  a syntax or {@code null} for best guess
  @return options with the syntax set