split

$group split: releases all elements, returns released elements
$group split yes: releases all elements recursively, returns released elements

obj method group split {{recursive no}} {
  if {$recursive} then {
    set result {}
    foreach obj [$self release all] {
      lappend result {*}[$obj split yes]
    }
  } else {
    set result [my elements]
    $self release all
  }
  set result
}