release

$group release element: releases element

obj method group release args {
  if {$args eq "all"} then {
    set args [my elements]
  }
  foreach element $args {
    set index [lsearch [my elements] $element]
    if {$index >= 0} then {
      my elements [lreplace [my elements] $index $index]
      $element group [$self group]
    }
  }
  set args
}