code: public CommandLine setUseSimplifiedAtFiles(boolean simplifiedAtFiles) {
          getCommandSpec().parser().useSimplifiedAtFiles(simplifiedAtFiles);
          for (CommandLine command : getCommandSpec().subcommands().values()) {
              command.setUseSimplifiedAtFiles(simplifiedAtFiles);
          }
          return this;
      }
docs: Sets whether to use a simplified argument file format that is compatible with JCommander.
  In this format, every line (except empty lines and comment lines)
  is interpreted as a single argument. Arguments containing whitespace do not need to be quoted.
  When system property {@code "picocli.useSimplifiedAtFiles"} is defined, the system property value overrides the programmatically set value.
  @param simplifiedAtFiles whether to use a simplified argument file format. The default is {@code false}.
  @return this {@code CommandLine} object, to allow method chaining
  @since 3.9