dots

$group dots: returns contained dots
$group dots show: applys method show to its dots

obj method group dots args {
  lappend result
  lappend options
  while {[string index $args 0] eq "-"} {
    set args [lassign $args option]
    if {$option eq "-gravity"} then {
      if {![$self constraint gravity]} then {
        lappend options $option
      }
    } else {
      lappend options $option
    }
  }
  set result [concat {*}[$self elements dots {*}$options]]
  lmap obj [lunique $result] {$obj {*}$args}
}