Untested code to illustrate the getter/setter functions I'm imagining.

ewiki_getvar($a_variable; $a_defvalue=FALSE){
  if(isset($_COOKIE*$a_variable){
    return($_COOKIE*$a_variable);
  }else{
    return($a_defvalue);
  }
}

ewiki_setvar($a_variable; $a_value; $a_vartype=*EWIKI_VARTYPE_SESSION?; $a_user=''){
   setcookie($a_variable, $a_value, ($a_vartype==*EWIKI_VARTYPE_SESSION)
     ? '':time()+7*24*3600, "/");
}