join '', map { $_, $hash{$_} } ( qw/ page chap / );

##</code><code>##

  { page => 'chappage', chap => '' },
  { page => '', chap => 'pagechap' },

##</code><code>##

  join "\0", map { $_, $hash{$_} } ( qw/ page chap / );

##</code><code>##

  join 'xyx', map { s/x/xx/g; $_ } map { $_, $hash{$_} }, qw/ page chap /;

##</code><code>##

  join 'xyx', map { s/x/xx/g; $_ } map $hash{$_}, qw/ page chap /;